Speed is the rate at which distance is travelled.
Speed answers: how fast is the object moving along its path?
It does not specify direction. A car moving east at and a car moving west at have the same speed but different velocities.
Instantaneous speed is the magnitude of instantaneous velocity. Average speed over a journey is total distance divided by total time and is not generally the magnitude of average velocity.
Formula / representation
For average speed over a journey:
For uniform motion in one direction, speed may be numerically equal to the magnitude of velocity.
Units