Seconds taken off the time of the first riders at a finish or an intermediate sprint, credited to the general classification.
Typically 10, 6 and 4 seconds to the first three at a stage finish, and 3, 2, 1 seconds at an intermediate sprint. Those seconds are subtracted from the rider's GC time.
In a tight race, bonuses can decide the winner: a leader will sometimes contest an intermediate sprint just to scrape three seconds off a rival.