In terms of HTTP communication, cookies are small pieces of text information sent by a web server to your browser and stored on your computer.
When you next visit the same website this data is sent back to the server. Cookies are normally used to distinguish you from other users, store your preferences, details about the items you wish to purchase in e-shops and for other similar purposes.
Technically, cookies are pieces of code gathered by your browser and sent back to the server you are interacting with to provide its operator with more details about your behaviour and preferences.
Cookies are not linked to your name or email address but may contain your login credentials. Cookies are common to a single browser session. Cookies are not secured or encrypted in any way, including the data they contain.