A cookie is a small block of data created by a web server while a user is browsing a website and placed on the users computer or other device by the users web browser. Cookies are used to store information about a users browsing activity, such as items added to a shopping cart or pages visited in the past. They can also be used to personalize a users experience on a website by storing preferences or login information. Cookies are created by the web server and stored on the client computer by the web browser. The browser then sends them back to the server with every request, introducing states (memory of previous events) into otherwise stateless communication. There are different types of cookies, including session cookies, which are only persistent while the user is navigating or visiting a given website, and third-party cookies, which are not restricted to the initial site. Cookies cannot be used by themselves to identify a user.