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Delta-v, or Δv, (literally, the change in speed) in astrodynamics, (how spacecraft move in space) is a measure of the amount of effort (pushing power) needed to change a craft's trajectory (how it's going to move from now on) in space. It is measured by a unit of speed.
Delta-v is calculated in meters per second of thrust, or m/s.
For example, to reach Low Earth orbit, (LEO) a spacecraft generally needs about 9,300 to 10,000 m/s of thrust.