Privacy Sandbox glossary

Privacy Sandbox articles and documentation assume a knowledge of concepts from privacy, advertising, and web development. This glossary explains key terms.

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Ad auction (FLEDGE)

In FLEDGE, an ad auction is run by a seller (ikely to be an SSP or maybe the publisher itself), in JavaScript code in the browser on the user's device, to sell ad space on a site that displays ads.

Ad creative, creative

The contents of the ad served to users. Creatives can be images, videos, audio, and other formats. Creatives live within an ad space, and are served by adtech within line items.

Ad exchange

A platform to automate buying and selling of ad inventory from multiple ad networks.

Ad inventory, ad space

The spaces for ads that are available from a site that sells ad space.

Ad platform (Adtech)

A company that provides services to deliver ads.

Advertiser

A company that pays to advertise its products.

Aggregatable reports

Encrypted reports sent from individual user devices. These reports contain data about cross-site user behavior and conversions. Conversions (sometimes called attribution trigger events) and associated metrics are defined by the advertiser or adtech. Each report is encrypted to prevent various parties from accessing the underlying data.

Attestation

A mechanism to authenticate software identity, usually with cryptographic hashes or signatures. For the aggregation service proposal, attestation matches the code running in the adtech-operated aggregation service with the open source code.

Attribution

Identification of user actions that contribute to an outcome.

For example, a correlation of ad clicks or views with conversions.

The rendering engine used by Chrome, developed as part of the Chromium project.

Buyer

A party bidding for ad space in an ad auction, likely to be a DSP, or maybe the advertiser itself. Ad space buyers own and manage interest groups.

Learn about ad space buyers in FLEDGE.

Chromium

An open-source web browser project. Chrome, Microsoft Edge, Opera and other browsers are based on Chromium.

Click-through rate (CTR)

The ratio of users who click on an ad, having seen it.

See also impression.

Click-through-conversion (CTC)

A conversion attributed to an ad that was 'clicked'.

Coarse data

Limited information provided by Attribution Reporting API event-level reports. This is limited to 3 pieces of conversion data for clicks and 1 piece for views. Specific, granular conversion data (such as specific prices of items and timestamps) are not included.

Conversion

The completion of some desired goal following action by a user.

For example, a conversion may occur with the purchase of a product or sign-up for a newsletter after clicking an ad that links to the advertiser's site.

A small piece of textual data that websites can store on a user's browser. Cookies can be used by a website to save information associated with a user (or a reference to data stored on the website's backend servers) as the user moves across the web.

For example, an online store can retain shopping cart details even if a user is not logged in, or the site could record the user's browsing activity on their site. See First-party cookie and Third-party cookie.

Coordinator

An entity responsible for key management and aggregatable report accounting. The coordinator maintains a list of hashes of approved aggregation service configurations and configures access to decryption keys.

Data management platform (DMP)

A software used to collect and manage data relevant for advertisers. These platforms help advertisers and publishers identify audience segments, which can then be used for campaign targeting.

Learn more about DMPs.

Demand-side platform (DSP)

An adtech service used to automate ad purchasing. DSPs are used by advertisers to buy ad impressions across a range of publisher sites. Publishers put their ad inventory up for sale through marketplaces called ad exchanges, and DSPs decide programmatically which available ad impression makes most sense for an advertiser to buy.

Differential privacy

Techniques to allow sharing of information about a dataset to reveal patterns of behaviour without revealing private information about individuals or whether they belong to the dataset.

Domain

See Top-Level Domain and eTLD.

eTLD, eTLD+1

Stands for effective top-level domains (TLD), which are defined by the Public Suffix List.

For example:

co.uk 
github.io
glitch.me

Effective TLDs are what allow foo.appspot.com to be a different site from bar.appspot.com. The eTLD in this case is appspot.com, and the whole site name (foo.appspot.com, bar.appspot.com) is known as the eTLD+1.

See also Top-Level Domain.

Entropy

A measure of how much an item of data reveals individual identity.

Data entropy is measured in bits. The more that data reveals identity, the higher its entropy value.

Data can be combined to identify an individual, but it can be difficult to work out whether new data adds to entropy. For example, knowing a person is from Australia doesn't reduce entropy if you already know the person is from Kangaroo Island.

Federated identity (federated login)

A third-party platform to allow a user to sign in to a website, without requiring the site to implement their own identity service.

Federated Credential Management API (FedCM)

Federated Credential Management API is a proposal for a privacy-preserving approach to federated identity services. This will allow users to log into sites without sharing their personal information with the identity service or the site.

FedCM was previously known as WebID, and is still in development in the W3C.

Fenced frame

A (<fencedframe>) is a proposed HTML element for embedded content, similar to an iframe. Unlike iframes, a fenced frame restricts communication with its embedding context to allow the frame access to cross-site data without sharing it with the embedding context.

Some Privacy Sandbox APIs may require select documents to render within a fenced frame. Learn more about the Fenced Frames proposal.

Fingerprinting

Techniques to identify and track the behaviour of individual users.

Fingerprinting uses mechanisms that users aren't aware of and can't control. Sites such as Panopticlick and amiunique.org show how fingerprint data can be combined to identify you as an individual.

Fingerprinting surface

Something that can be used (probably in combination with other surfaces) to identify a particular user or device.

For example, the navigator.userAgent() JavaScript method and the User-Agent HTTP request header provide access to a fingerprinting surface (the User-Agent string).

First-party

Resources from the site you're visiting.

For example, the page you're reading is on the site developer.chrome.com and includes resources requested from this site. Requests for those first-party resources are called 'first-party requests'. Cookies from developer.chrome.com stored while you're on this site are called first-party cookies.

See also Third-party.

Cookie stored by a website while a user is on the site itself.

For example, an online store might ask a browser to store a cookie in order to retain shopping cart details for a user who is not logged in. See also Third-party cookies.

I2P

Intent to Prototype. The first stage in developing a new feature in Blink. The announcement is posted to the blink-dev mailing list with a link to the proposal for discussion.

I2E

Intent to Experiment. Announcement of a plan to make a new Blink feature available to users for testing, typically through an origin trial.

I2EE

Intent to Extend Experiment. Announcement of a plan to extend the duration of an origin trial.

I2S

Intent to Ship. Announcement of a plan to make a new feature of Blink available to users in stable versions of Chrome.

Impression

Could refer to either:

  • View of an ad. See also click-through rate.
  • An ad slot: the HTML markup (usually <div> tags) on a web page where an ad can be displayed. Ad slots constitute inventory.

Inventory

The ad slots available on a site. Ad slots are the HTML markup (usually <div> tags) where ads can be displayed.

k-anonymity

A measure of anonymity within a data set. If you have k anonymity, you can't be distinguished from k-1 other individuals in the data set. In other words, k individuals have the same information (including you).

Nonce

Arbitrary number used once only in cryptographic communication.

Origin

Defined by the scheme (protocol), hostname (domain), and port of the URL used to access it.

For example: https://developer.chrome.com

Origin trial

Trials provide access to a new or experimental feature, to make it possible to build functions that users can try out for a limited time before the feature is made available to everyone.

When Chrome offers an origin trial for a feature, an origin can be registered for the trial to allow the feature for all users on that origin, without requiring users to toggle flags or switch to an alternative build of Chrome (though they may need to upgrade). Origin trials allow developers to build demos and prototypes using new features. The trials help Chrome engineers understand how new features are used, and how they may interact with other web technologies.

Find out more: Getting started with Chrome's origin trials.

Passive surface

Some fingerprinting surfaces—such as User-Agent strings, IP addresses, and Accept-Language headers—that are available to every website, whether the site asks for them or not.

Passive surfaces can easily consume a site's privacy budget.

The Privacy Sandbox initiative proposes replacing passive surfaces with active ways to get specific information, for example using Client Hints a single time to get the user's language rather than having an Accept-Language header for every response to every server.

Publisher

In the Privacy Sandbox context, a site with ad space that is paid to display ads.

Reach

The total number of people who see an ad or who visit a web page that displays the ad.

Real-time bidding (RTB)

An automated auction for buying and selling ad impressions on websites, completed during page load.

Remarketing

Advertising to people who've already visited your site on other sites.

For example, an online store could show ads for a toy sale to people who previously viewed toys on their site.

Reporting origin

The entity that receives aggregatable reports—in other words, the adtech that called the Attribution Reporting API. Aggregatable reports are sent from user devices to a well-known URL associated with the reporting origin.

Seller

The party running an ad auction, likely to be an SSP or maybe the publisher itself.

Site

See Top-Level Domain and eTLD.

Summary report

An Attribution Reporting API and Private Aggregation API report type. A summary report includes aggregated user data and detailed conversion data, resulting from noisy aggregation applied to aggregatable reports. The summary includes aggregated user data and detailed conversion data.

Summary reports were formerly known as aggregate reports.

Supply-side platform, Sell-side platform

An adtech service used to automate selling ad inventory. SSPs allow publishers to offer their inventory (empty rectangles where ads will go) to multiple ad exchanges, DSPs, and networks. This enables a wide range of potential buyers to bid for ad space.

Surface

See Fingerprinting surface and Passive surface.

Third-party

Resources served from a domain that's different from the website you're visiting.

For example, a website foo.com might use analytics code from google-analytics.com (via JavaScript), fonts from use.typekit.net (via a link element) and a video from vimeo.com (in an iframe). See also First-party.

Cookie stored by a third-party service.

For example, a video website might include a Watch Later button in their embedded player to allow a user to add a video to their wishlist without forcing them to navigate to the video site.

See also First-party cookie.

Top-level domain (TLD)

Top-level domains such as .com and .org are listed in the Root Zone Database.

Note that some 'sites' are actually just subdomains. For example, translate.google.com and maps.google.com are subdomains of google.com. These subdomains are eTLD + 1.

Trusted Execution Environment (TEE)

A special configuration of computer hardware and software that allows external parties to verify the exact versions of software running on the computer. TEEs allow external parties to verify that the software does exactly what the software manufacturer claims it does—nothing more or less.

To learn more about TEEs used for the Privacy Sandbox proposals, read the FLEDGE services explainer and the Aggregation Service explainer.

User-Agent string

An HTTP header used by servers and network peers to request indentifying information about an application, operating system, vendor, or version of a user agent. The User-Agent string broadcasts a large string of data, which is problematic for user privacy. User-Agent reduction is proposed to remove sensitive information and reduce passive fingerprinting.

User-Agent Client Hints (UA-CH)

Provide specific pieces of the User-Agent string on explicit request. This helps reduce passive surfaces in the User-Agent string which may lead to user identification or covert tracking.

UA-CH is sometimes referred to as "Client Hints."

.well-known

A file used to add redirects to a website from standardized URLs.

For example, password managers can make it easier for users to update passwords if a website sets a redirect from /.well-known/change-password to the change password page of the site.

In addition, it can be useful to access policy or other information about a host before making a request. For example, robots.txt tells web crawlers which pages to visit and which pages to ignore. IETF RFC8615 outlines a standardized way to make site-wide metadata accessible in standard locations in a /.well-known/ subdirectory.

See a list of recommendations for .well-known at iana.org/assignments/well-known-uris/well-known-uris.xhtml.

Worklet

A worklet allows you to run specific JavaScript functions and return information back to the requester. Within a worklet, you can execute JavaScript but you cannot interact or communicate with the outside page.

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