Percent front braking is the "brake bias" - the percentage of total braking that is done by the front wheels. If the front wheels do 70% of the total braking and the rear brakes do 30% then that's 70%.
Ax = acceleration; the "Ax / g" term is the total braking expressed as a fraction of a "g force" (the force of gravity). In metric units, the gravitational constant is 9.81 m/s2. If your deceleration is at 7 m/s2 then the "Ax / g" term = (7.0 / 9.81).
Outboard brakes are brakes mounted at the wheel hubs - the usual arrangement - as opposed to "inboard brakes" which are mounted inboard beside a (fixed-to-the-chassis) differential. The distinction is that the braking torque of conventional "outboard brakes" is transmitted to the bodyshell through the suspension linkage. Inboard brakes transmit that torque directly to the bodyshell bypassing the suspension linkage and the torque gets from the wheel to the inboard brake via a shaft with universal joints.
