The product of mass and velocity is called momentum. It is denoted by 'p'.
p = m×v.
Ex. A pen at stationary position and a pen through at a velocity known as Momentum.
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Momentum is the quantity of motion possessed by a moving body.
Momentum is directly proportional to the mass and velocity of the body, and inversely proportional to the time.
That is, Momentum = Mass × velocity
 or,          p = mv, where p is momentum, m is mass and v is velocity.

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how its inversely proportional to time
Because if momentum increases, then time decreases