Speed is a mesure of how fast something is moving it can be calculated using the formula .
The unit of speed is meters per second (m/s) but can also be kilometers per hour (km/h).
For example if a runner ran 100 meters in 10 seconds they would be running at 10m/s.
Speed is a scalar quantity whereas velocity is the vector equivalent of speed. This means speed does not have direction whereas velocity is speed with a direction. Exam questions often ask both for both the speed and velocity. Note that they are often different if this is asked.