Wave speed is defined as the distance a wave travels in a specified length of time. This measurement is calculated by picking a certain point on a wave and recording how far that point travels in the time given.
The speed of a wave can be affected by the material through which it travels. Additionally, a material's elasticity and temperature can speed up or slow down the wave. The material though which a wave travels is known as the medium. Not all waves require a medium for travel. Those that require a medium are known as mechanical waves, while those that don't are known as electromagnetic waves.