VAM is an acronym for the Italian phrase 'velocità ascensionale media,' which translates to English as 'average ascent speed.' The term was coined coined by Dr Michele Ferrari

Michele Ferrari

Michele Ferrari is an Italian physician, cycling coach and author.-Biography:Ferrari was born in Ferrara, Emilia-Romagna, where he still lives...

 and is the speed of elevation

Elevation

The elevation of a geographic location is its height above a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface ....

 gain, usually stated in units of meters per hour. VAM is a parameter used in cycling as a measure of fitness and speed; it is useful for relatively objective comparisons of performances and estimating a rider's power output per kilogram of body mass, which is one of the most important qualities of a cyclist who competes in stage races and other mountainous events.