What does L10 life mean in bearing selection?

L10 life (or B10 life) is the rating life in million revolutions at which 90% of a group of identical bearings will survive (10% will fail due to fatigue). It is calculated using the formula L10 = (C/P)^p, where C is dynamic load rating, P is equivalent dynamic load, and p is 3 for ball bearings and 10/3 for roller bearings. This statistical measure helps engineers predict bearing replacement intervals.