Noun
In singing, or in the use of the bow, a gradual carrying or lifting of the voice or sound very smoothly from one note to another; a gliding from tone to tone.
Source: Webster's dictionaryA player can use this to create a vibrato or a portamento effect. Source: Internet
String harmonic glissandi are discussed pp. 132-33; horn glissandi pp. 252-254 'Continuous glissando' or portamento Musical instruments with continuously variable pitch can effect a portamento over a substantial range. Source: Internet
The latter could thus be thought of as capable of either 'glissando' or 'portamento', depending on whether the drum was rolled or not. Source: Internet
The portamento circuitry employs a fixed slide time, meaning that whatever the interval between notes, the time taken to reach the correct pitch is always the same. Source: Internet