Cookies are messages sent to the browser by a web server and stored in a text file on the visitor’s computer.

Recorded data in cookies can then be used by merchants to optimize their websites according to the user’s preferences. Cookies are usually stored 30 days in a user’s browser, or less, if cookies are manually cleared by the user before.

For affiliates, cookies are invaluable since they are used to track where the visitor came from (geo/device) and how much time elapsed between the first visit and the click-through/lead/sale.