(1) A type of MIDI data (range 1 to 127) usually used to indicate how quickly a key was pushed down (attack velocity) or allowed to rise (release velocity). A Note-On message with a velocity value of 0 is equivalent to a Note-Off message.
(2) The velocity of sound: The speed at which sound waves propagate. The precise speed will depend on the density of the medium through which the sound waves travel: in air, at sea level and at 0˚C with 30% relative humidity, this is approximately 1088 ft/sec. (331.7 m/sec.) At average room temperatures it is slightly faster.