What are cookies?

A web cookie is a piece of text information , stored by the browsers for authentication purposes, storing site preferences, storing shopping cart contents, acts as an identifier for a server-based sessions, etc...

Well, it is information which store by browser, so that not all information they need to load each time you open the same site.

Cookies are small files which are stored on a user's computer. They are designed to hold a modest amount of data specific to a particular client and website, and can be accessed either by the web server or the client computer. This allows the server to deliver a page tailored to a particular user, or the page itself can contain some script which is aware of the data in the cookie and so is able to carry information from one visit to the website (or related site) to the next.

temporary files

It contains information which helps navigate through a website.

Cookies are messages that web servers pass to your web browser when you visit Internet sites. Your browser stores each message in a small file, called cookie.txt. When you request another page from the server, your browser sends the cookie back to the server. These files typically contain information about your visit to the web page, as well as any information you've volunteered, such as your name and interests.

The term "cookie" is an allusion to a Unix program called Fortune Cookie that produces a different message, or fortune, each time it runs.
http://kb.iu.edu/data/agwm.html

This is the information stored by our browser it cannot store every thing we can delete them if not required.

Temporary files.

In Computer, Cookies is small text files. Various information can be stored in this file.
There are two types of cookies - Temporary (stored for a short time) and Permanent (stored for a long time)

Temporary file stored on your system for tracking purposes