What is an HTTP cookie used for?

A cookie is a code used by a client to authenticate a person's identity to an HTTP server.

Cookies are used at the end of a transaction, to indicate the end of the transaction

A cookie is used to spoof client identity to an HTTP server.

A cookie is a code used by a server, carried on a client's HTTP request, to access information the server had earlier stored about an earlier interaction with this Web browser. $[$Think about the distinction between a browser and a person.$]$

A cookies is a code used by a server, carried on a client's HTTP request, to access information the server had earlier stored about an earlier interaction with this person. $[$Think about the distinction between a browser and a person.$]$