Proper speed may refer to:

In common everyday speech, speed of sound refers to the speed of sound waves in air.

The speed you refer to when you say that the "tail" of a wave packet overtakes the "head" refers to the 'phase velocity'.

The 'speed of light' in this article refers to the speed of all electromagnetic radiation in vacuum.

In a more physically correct sense, the "speed of gravity" refers to the speed of a gravitational wave.

Need for speed may refer to:

Radial speed may refer to:

The speed of the bus, measured in megahertz (MHz), refers to how much data can move across the bus simultaneously.

Pumping speed refers to the volume flow rate of a pump at its inlet, often measured in volume per unit of time.

The normal stall speed, specified by the V values above, always refers to straight and level flight, where the load factor is equal to 1g.