* Mass is a scalar quantity. It only has magnitude (how much mass there is) and no direction.

* Acceleration is a vector quantity. It has both magnitude (how quickly velocity changes) and direction (the direction of the change in velocity).

Key Concepts:

* Scalar: A quantity that only has magnitude (size). Examples: temperature, speed, time, mass.

* Vector: A quantity that has both magnitude and direction. Examples: displacement, velocity, acceleration, force.