Newton's second law of motion involves the effect of force acting on a mass.
It has to be understood that this actually means the combination of any and
all individual forces acting on it, with their individual strengths and directions
all added together.
When all the individual forces acting on an object add up to zero, then the
whole group of forces is said to be 'balanced'.
When all the individual forces acting on an object don't add up to zero, then
the whole group of forces is said to be 'unbalanced'.
Notice that there's no such thing as 'a balanced force' or 'an unbalanced force'.
It's a group of two or more forces that's balanced or unbalanced.
