Question

unlike velocity, speed is scalar, which means it is described by only.

Explanation:

In physics (a subfield of Natural Science), scalar quantities are described by magnitude (or size) only, while vector quantities (like velocity) have both magnitude and direction. Since speed is a scalar, it is described by magnitude (or a numerical value representing how fast an object is moving) only.

Answer:

magnitude (or size, or a numerical value representing how fast an object is moving)