What are tracking cookies?

What's a cookie?

A cookie consists of a packet of data sent by an Internet server to a browser, which is returned by the browser each time it subsequently accesses the same server, used to identify the user or track their access to the server.

What are tracking cookies?

Many websites earn money from marketing research groups that place a unique identifying cookie on your computer that is read by any site using that particular marketing service. The marketing service can then identify which of their contracted sites you have visited in the past in order to send you targeted advertising that is specific to you as an individual.

This allows advertising services to piece together a "profile" of your interests.