What does acceleration refer to?

Acceleration refers to the rate at which velocity changes over time. This means it quantifies how quickly an object's speed or direction is increasing or decreasing. For instance, when a car speeds up, slows down, or changes its direction while moving, it is experiencing acceleration. Acceleration is measured in units of meters per second squared (m/s²) and can encompass changes in both the magnitude of velocity (speed) and its direction.

In contrast, speed simply measures how fast an object is moving without regard to direction, while the distance covered pertains to how far an object travels, irrespective of its change in velocity. Direction of motion, meanwhile, describes where an object is heading, but does not directly relate to the concept of acceleration itself. Thus, the correct definition of acceleration aligns with the understanding of it as a change in velocity over time.