It is a vector. The units are the same as for average speed. The average acceleration of an object is its change in velocity divided by the time required to make the change. It is a vector and has the same direction as the change in velocity. In equation form average acceleration is where is the final velocity and is the initial velocity.
Examples Consider an object traveling to the right.
A positive answer indicates that the acceleration is to the right. The time is still 10 s. The minus sign indicates that the acceleration is to the left. Next consider an object traveling to the left. A negative answer indicates that the acceleration is to the left.