Also known as web cookies, browser cookies or HTTP cookies, a cookie is a tiny piece of data sent out by websites to be stored in a user’s browser while that user is visiting and browsing a website. Designed to be a dependable means of recording the current state of a website or the behavior of a user while on the site, cookies are also used by many site operators to construct a longer term record of a users’ browsing history and online activities.

Many essential functions of the modern Internet are cookie-dependent, including the use of authentication cookies by web servers to detect whether or not a user is logged in, which account they are logged in under, and other details. Without such information, the server would not know whether it is safe to transmit sensitive data to the user, or whether to prompt the user to log in.

Specific types of cookies include session cookies (which exist only so long as the user is browsing and navigating the website), persistent cookies (cookies that outlast user sessions and can last for long periods of time), secure cookies, third-party cookies, super-cookies and zombie-cookies.