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 platform (Adtech)
A company that provides services to deliver ads.
A company that pays to advertise its products.
Identification of user actions that contribute to an outcome. For example: correlation of ad clicks or views with conversions.
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.)
A conversion attributed to an ad that was 'clicked'.
The completion of some desired goal following action by a user. For example, purchase of a product or sign-up for a newsletter after clicking an ad that links to the advertiser's site.
A website can ask a web browser to store a small piece of textual data (called a cookie) on a user's computer. Cookies can be used by a website to save data about 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.
Techniques to enable sharing of information about a dataset to reveal patterns of behaviour without revealing private information about individuals or whether they belong to the dataset.
Effective Top Level Domains are defined by the Public Suffix List. For example:
Effective TLDs are what enable foo.appspot.com to be a different site from bar.appspot.com. The effective top-level domain (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.
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 (also known as federated login)
A third-party platform to enable a user to sign in to a website, without requiring the site to implement their own identity service.
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.
Something that can be used (probably in combination with other surfaces) to identify a particular user or device. For example, the
User-Agent HTTP request header provide access to a fingerprinting surface (the user agent string).
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 that site. Requests for those first-party resources are called 'first-party requests', and 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.
- View of an ad. (See also click-through rate.)
- An ad slot: an empty rectangle on a web page where an ad can be displayed. Ad slots constitute inventory.
The ad slots available on a site: the empty rectangles where ads can be displayed.
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).
Arbitrary number used once only in cryptographic communication.
The origin of a request, including the scheme and server name, but no path information. For example:
Origin trials provide access to a new or experimental feature, to make it possible to build functionality 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 enable the feature for all users on that origin, without requiring users to toggle any flags or switch to an alternative build of Chrome (though they may need to upgrade). Origin trials enable developers to build demos and prototypes using new features. The trials also 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.
Some fingerprinting surfaces, such as user agent strings, IP addresses and accept-language headers, are available to every website whether the site asks for them or not. That means 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.
In the Privacy Sandbox context, a site that displays ads.
The total number of people who see an ad (or who visit a web page that displays the ad).
Reaching people on other sites who have previously visited your site. For example, an online store could show ads for a toy sale to people who previously viewed toys on their site.
Cookie stored by a third-party service. For example, a video website might include a Watch Later button in their embedded player, to enable 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 just subdomains of google.com (which is the eTLD + 1).
It can be useful 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. You can see a list of these at iana.org/assignments/well-known-uris/well-known-uris.xhtml.