Cookies are variables that can be stored on a user's computer and be picked up by any other web pages in the correct domain and path. Cookies are set to expire after a certain length of time. They are limited to storing string values only.
Cookies can identify the computer being used, not the individual.
The most modern browser is expected to be able to store at least 300 cookies of four kilobytes (4 kb) per server or domain.
For each domain and path, you can store upto 20 cookies.
Cookies cannot access by any other computer except the visitor's computer that created the cookie.
A website can set and read only its own cookies (for example, Yahoo can’t read IE's cookies).
During the browsing session browser stores the cookies in memory, at the time of quitting they goto the file called cookies.txt. Different browser store cookies files in a different location in the disk.
There are six parts of a cookie : name, value, expires, path, domain, and security. The first two parts i.e. name and value are required and rest parts are optional.