Velocity

Velocity is a measure of how fast something moves in a particular direction. To define it needs both magnitude and direction. If an object moves east at 9 metres per second (9 m/s), then its velocity is 9 m/s to the east.

The idea behind this is that speed does not tell us in which direction the object moves in a given frame of reference. Speed is one part of velocity, direction is the other part. Depending on the frame of reference, the velocity can be defined with many mathematical concepts required for making the correct analysis.