This billion pool is for predicting the date at which the number of articles (as defined by the official article count presented on the Special:Statistics) in the English Wikipedia reaches 1,000,000,000 (one billion). The person who comes closest to the actual date is the winner (of eternal fame). The current number of articles in the English Wikipedia is 6,879,404.
This pool will be closed for entries when the English Wikipedia article count reaches 800,000,000 (80%), so be sure to place your guess before then.