Base attack bonus

A base attack bonus (BAB) is an attack roll bonus derived from character class and level. Base attack bonuses increase at different rates for different character classes (see base attack bonus progression). A character gains a second attack when his or her base attack bonus reaches +6, a third with a base attack bonus of +11 or higher, and a fourth with a base attack bonus of +16 or higher. Base attack bonuses gained from different classes, such as when a character is a multiclass character, stack.