A clickstream is an electronic log or record of a users Internet activity. It includes HTTP data such as URL's visited, browser type, how long a user accessed a web page, referrer details etc.. ISP's typically do not sell your name, but do identify you as a specific user.
Many ISP's resell clickstream data to Internet marketing companies. The price per user, per month has been reported as US$0.40 cents.
Sources: Seeking Alpha and
Clickstream data mart