describes how fast an object is moving.

The quantity that “describes how fast an object is moving” is speed.

Quick Scoop

What is speed?

• Speed tells you how fast an object covers distance over time.

• In simple terms:
  speed=distancetime\text{speed}=\dfrac{\text{distance}}{\text{time}}speed=timedistance​.

• If something covers a large distance in a short time, it has a high speed; if it covers only a small distance in the same time, it has a low speed.

Speed vs. velocity (common pair in questions)

Many textbook or quiz items pair this phrase with velocity :

• Speed describes how fast something is going.

• Velocity describes how fast something is going and in what direction (for example, 10 m/s east).

So if your item is a fill‑in‑the‑blank like:

“________ describes how fast an object is moving.”

…the correct word is speed. TL;DR: The term that describes how fast an object is moving is speed.

Information gathered from public forums or data available on the internet and portrayed here.