Which is not a way to accelerate an object?
a. speed it up
c. change its direction
b. slow it down
d. apply balanced forces

Acceleration is the word that describes any of the changes in 'a', 'b', or 'c'.

When the group of all forces on an object is balanced, the effect on the object is
the same as if there were no forces acting on it at all.  Under those circumstances,
the object's acceleration is zero.  Its speed and direction of motion stay constant.