Musical instruments, including the voice, produce sound by causing some body to vibrate. A musician might pluck or bow a string, strike some surface, or blow through a reed; the acoustical signal that these vibrations produce has a number of distinctive properties (frequency, amplitude, etc.). Pitch is the property of a sound that is based upon its frequency (in contrast to properties such as loudness or timbre). The faster the frequency, the higher the pitch, and vice versa.
Framed in a less technical way, pitch is the property of a note that distinguishes it from another note without reference to volume or instrument. It is the property that allows us to perceive the difference between, say, the notes C and D, or between middle C and high C, regardless of instrument, voice, or volume.
Beginning in the twentieth century, it has been conventional Western practice to standardize the frequency for each pitch. The frequency of 440 hertz is assigned to the A above middle C; the frequencies of other pitches are calculated in relation to frequency. In the audio clip below, of the sound of an orchestra tuning before playing, we hear about one hundred different instruments all hovering about a single pitch known as A440.
Pitch is essentially a piece of “raw data” about some sound. As such, information about pitch need not be connected to a musical context. However, musicians routinely use the term “pitch” to refer to a musical note existing in the Western twelve-note system. (Musicians who have “perfect pitch,” also called “absolute pitch,” are capable of recalling and reproducing the frequency associated with a note. More commonly, musicians have a sense of “relative pitch,” meaning that they can aurally infer the sound of some note in relation to a given note, but cannot reliably recall or reproduce a note’s frequency “out of thin air.”)