An HTTP cookie or cookie is a special text, often encoded, sent by a server to a web browser and then sent back (unmodified) by the browser each time it accesses that server. Cookies are used for authentication as well as for tracking user behavior; typical applications are remembering user preferences and implementing the "shopping cart" system.
The term "cookie" is an English word (biscuit, pronunciation: /ˈkuˌki/). In computer science it is derived from the term "magic cookie", a concept often used in IT. In general, the word "cookie" with this meaning is also used in other languages; only in French-speaking technical terminology has an attempt been made to translate it by the term témoin ("witness").
Cookies have caused concern because they allow the collection of information about user behavior (basically, what web pages they visit and when). As a result, their use (and the information collected) is subject to legal restrictions in some countries, including the United States of America and EU countries. "Cookie" techniques have also been criticized for the fact that user identification is not always accurate, as well as for the fact that computer attacks can be carried out through them.
There are also a number of misconceptions about cookies, most based on the (wrong) impression that they always contain executable code; in reality they are just texts, and cannot perform any operation. They are neither spyware nor computer viruses, although some antivirus and anti-spyware programs can detect them.
Most modern browsers allow the user to decide whether or not to accept cookies. However, the sites that refuse them will lack certain facilities - for example, in a virtual store it will no longer be possible to use the shopping basket, if it has been implemented with the help of cookies.
