Here's a breakdown:

* Acceleration is the rate of change of velocity over time. It tells us how quickly the velocity is changing.

* Positive acceleration means velocity is increasing. The object is speeding up.

* Negative acceleration means velocity is decreasing. The object is slowing down. This is also known as deceleration.

Important Note: Negative acceleration doesn't necessarily mean the object is moving in the negative direction. It simply means the velocity is becoming less positive (or more negative).

For example, a car braking to a stop has a negative acceleration, even though it might be moving in the positive direction.