Delta-v (Δv) is a physics term used in astronautics and aeronautics to describe a change (delta) in velocity (v). Delta-v is the end result of an acceleration over time.
Perhaps the most common use of the term is when discussing orbits. To move from one orbit to another requires a change in velocity, typically provided by the thrust of a rocket engine. Since rocket fuel is expensive and heavy, considerable study is put into reducing the total delta-v needed over a satellite's life-span.
