Base Attack

From RPF - The "Script"

Base attack is a stat determined by a Class. Each class has a different Base Attack rate. At level 1 this stat is equal to the Base Attack rate (i.e. 1 for a Fighter). The stat will increase by the class's Base Attack rate each level.

When used in any formula (such as Attack) the rate is always rounded down (so 1.5 only counts as 1).