A cookie is a small and very simple text file saved on the user's computer disk drive at the request of the server managing the website being visited. It contains information about the user's navigation on the site pages. The original idea was to make subsequent use of the site by the same person easier. Thus, if Sally returns to a site where she has already filled in a form with her name and surname, she will be welcomed with "Hello, Sally". Apart from saying hello, a cookie is used to store the preferences chosen by a user during a visit (this is what the Google search engine does for example).
On the user's computer cookies are managed by the browser (Internet Explorer, Firefox, Chrome, Safari, etc.). The browser receives the order from the server to save the cookies (the principle of cookies is included in the HTTP protocol used for exchanges on the web). The browser saves them and also enables them to be controlled according to what the user wants. Saving cookies can also be disabled (but then access to many sites, or at least to the use of their features, becomes impossible). Browsers allow cookies to be found (they are saved in deeply embedded sub-folders), to be listed and even to be selectively deleted. But if they are not deleted they eventually disappear because they have a date limit which can be several months or which can be at "end of session", i.e. the moment when the user leaves the site.
Cookies for advertising
Cookies are also widely used by advertisers who have built a complex and effective system. On the web pages of many sites, the areas reserved for advertising are sold to space brokers who have many clients. When a user displays a site page a cookie indicates the latest searches carried out by the person to the broker. If the user has shown a lot of recent interest in vacuum cleaners, they will have advertisements for this type of appliance displayed.
A cookie placed at the request of Futura, located by Firefox. This will expire when the user leaves the site (it expires at the end of the session). © Futura-Sciences