Answer:
Both speed and direction
Explanation:
Most people use both terms (velocity and speed) as if they were the same thing. But the reality is that this concepts are different , specially in physics.
Speed is a scalar quantity that refers to how fast an object is moving. It can be calculated as distance divided by time.
[tex]Speed=\frac{distance}{time}[/tex]
Velocity is a vector, and is the rate at which an object changes position in a certain direction. Because the direction is important here, velocity uses displacement instead of distance:
[tex]Velocity=\frac{displacement}{time}[/tex] in a direction
(Speed is based on a distance, and velocity is based on displacement, and the major difference is that velocity deals with direction, and speed has no direction).
The conclusion we can take from all of this is that the velocity can be defined as the speed with direction. So the velocity needs both speed and direction. Otherwise, the speed is a scalar quantity and it can only be defined with its value.
