The sawtooth wave (or saw wave) is a kind of basic non-sinusoidal waveform. It is named a sawtooth based on its resemblance to the teeth on the blade of a saw.
The usual convention is that a sawtooth wave ramps upward as time goes by and then sharply drops. However, there are also sawtooth waves in which the wave ramps downward and then sharply rises. The latter type of sawtooth wave is called a 'reverse sawtooth wave' or 'inverse sawtooth wave'. The 2 orientations of sawtooth wave sound identical when other variables are controlled.