Here's why:

* Magnitude: Acceleration has a magnitude, which tells us how quickly the velocity is changing.

* Direction: Acceleration also has a direction, which tells us the direction of the change in velocity.

For example, if a car is speeding up in a straight line, its acceleration is in the same direction as its motion. But if the car is slowing down, its acceleration is in the opposite direction to its motion. If the car is turning, the acceleration is directed towards the center of the curve.

In summary, acceleration has both magnitude and direction, making it a vector quantity.