Base attack bonus

The Base attack bonus or BAB is an addition to a character's attack rolls, based on their character class and level. It increases at different rates, depending on the class. Once the BAB reaches +6, a character may attempt a second attack each round of combat. Further attacks are gained when the BAB reaches +11 and +16. If a character has multiple classes, e.g. when they are multiclassing, their bonuses stack.
BABs are not formally defined within the D&D 4e OGL or [[SRD]] but references are made to BABs.