What does a cookie do in online advertising?

In the context of online advertising, a cookie primarily functions to communicate information back to a server. When a user visits a website, cookies are created and stored in the user's browser to track various types of information. This can include details such as login sessions, user preferences, and tracking data. By sending this information back to a server, advertisers can gather insights about user behavior, tailor advertisements, and optimize marketing strategies based on user interactions. This ability to communicate user-related data is a fundamental aspect of how digital advertising operates, enabling more personalized experiences and targeted advertising initiatives.

The other options, while related to the use of data in online contexts, do not accurately describe the primary function of cookies in the realm of online advertising. Cookies do not encrypt user data; instead, they store information that can be accessed by the server. They do store user preferences, but this is a function rather than the primary purpose as related to advertising. Measuring user engagement is a goal of using cookies, but again, it’s not the function of the cookie itself; rather, it’s the outcome derived from the information cookies are designed to communicate.