The term that explains an object's velocity has increased or decreased over time is acceleration.

Here's why:

* Velocity is a measure of both speed and direction.

* Acceleration is the rate of change of velocity. This means that if an object's velocity is changing (either in speed or direction), it is accelerating.

Examples:

* A car speeding up is accelerating.

* A car slowing down is also accelerating (in this case, decelerating).

* A car turning a corner is accelerating because its direction is changing.