Cookie

A small file, or bit of text, placed on your computer by your web browser at the request of a web server.

We often expect web servers to remember us when we make a return visit. For example, when we make a second purchase at a web store, we may want the server to remember our shipping address. We may expect a chat room to remember our "handle" or chat room nickname.

But when we connect to a web site, by default, no useful information about is is sent to the server. All the server knows is our computer's IP address. Since IP addresses are often re-used and reassigned by ISPs, and more than one person can use a particular computer, this isn't a useful way of recognizing repeat visitors.

That's why cookies were invented. When we provide information to a web site, by filling in a form or entering other text, the web server may choose to store some or all of that information on our computer in a cookie. The next time we visit the site, the web server can recall that information by asking our web browser for any cookies stored by that server.

Some people feel cookies are a security risk. I think otherwise. If cookies didn't exist, web servers would store the information we provide them on their own disks, were we can't see or change what they've remembered. 

Also, since a particular web server can only see cookies it created, cookies don't allow web servers to recall any information we didn't volutarily give them. If you don't want personal data stored in a cookie, don't tell it to a web site. But if you do tell personal information to a web site, cookies won't allow that information to spread to other locations.