What they are
A cookie is a piece of data that a Web server gives to a Web browser.
When the same browser asks the server for another page, it includes the
cookie with the request. This lets the server know when a sequence of
clicks all come from the same browser.
And that is all cookies do. Using cookies doesn't give the server
any personal information about the person visiting the Web site.
Why we use them
When someone arrives at a store, we give them a unique cookie.
When they click on an Order button, we use the cookie to decide
what shopping basket to put the product into.
(or some equivalent approach like putting a tracking code in the URL
for each visitor), there is simply no way to make a shopping basket work;
unless the server has some way to tell that two clicks on the Order button
are coming from the same browser, it has no way to know that both orders
should go into the same shopping basket.
Note that Yahoo! doesn't store any information in the cookies themselves.
The cookies are simply ids. Any information that shoppers enter when
placing an order is kept on our servers; the id in the cookie is merely
To learn more
Please see Netscape's document entitled Cookies and Privacy or their technical
specification for cookies if you would like a more in-depth treatment.