What is Bullet chess?

A game with a time control of less than 3 minutes is "bullet" chess. Bullet is one of the rating categories in your personal profile or 'finger'.

The exact boundary between "bullet" and "blitz" is defined by "etime < 3". etime is the time + 2/3 increment.
A bullet game is 0 1,  0 2,  0 3,  0 4,  1 0,  1 1,  1 2,  2 0  or  2 1.
Bullet time control games count towards your bullet rating, not your blitz rating. Games played in the 1-minute pool count towards the 1-minute rating, not the bullet rating.
For more information read "help bullet" and "help etime"