In the HTTP protocol, a cookie refers to a small amount of data that servers send to the browser. This is stored on the user's computer.
The browser then sends this data back to the server each time you visit the site. Cookies are commonly used to distinguish individual users, storing the contents of "shopping baskets" in electronic shops, user preferences, etc.
Technically, they are a series of codes by which the browser collects and then sends information about our behaviour back to the relevant server.
Cookies contain information about how long the browser should keep them (from one-off to several years).
Cookies are not directly linked to your name or email address, but often contain your login details to the system. They are common to a single browser installation. Cookies are not secured in any way and this includes the data collected.