The frequency content of a sound or audio signal often displayed as a graphic representation of amplitude against frequency. Three-dimensional displays of a spectrum add the time variation on the third axis. The spectrum of a sound is a primary determinant of its perceived timbre.
A partial spectrum consists of discrete frequencies known as overtones, harmonics or inharmonics. A continuous spectrum consists of noise components. The spectrum of a sound may be determined by a number of sound analysers or by Fourier analysis and is distributed over the audible range (20 to 20,000 Hz). A partial spectrum is also known as a line spectrum, where discrete frequencies are present. A continuous spectrum, on the other hand, shows frequencies continuously distributed over the audible range. (Source - Barry Truax - Handbook for Acoustic Ecology CD-ROM Edition. Cambridge Street Publishing, 1999 - CSR-CDR 9901)