Cookies are small text files which most websites store on the user’s device when a webpage is viewed. It usually contains basic information such as server name, lifetime and a value, which is a randomly generated unique number.
With every subsequent visit, the webpage will attempt to read the information from a previously stored cookie and to “recognize” the user. When a cookie is successfully read, the operating system and web browser are identified and together this information can be used to provide the user with customized content, format the webpage properly, and prepare statistical information regarding the page visits.
Only the website which stores the cookie can make use of it.
More information about cookies can be found on the internet.