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

Here's why:

* Velocity is a vector quantity, meaning it has both magnitude (speed) and direction.

* Acceleration is the rate of change of velocity over time.

* Positive acceleration means the velocity is increasing.

* Negative acceleration means the velocity is decreasing (sometimes called deceleration).

Let me know if you'd like more explanation on any of these concepts!