Actually science (physics) defines it as the quantity of motion of a moving body, measured as a product of its mass and velocity, or p = mv. We, humans define it as the force that allows something to grow stronger or faster as time passes. The universe (aka science) does not care or know anything about growing stronger or faster as from its perspective there is no “stronger” or “faster” there is only p=mv. Stronger and faster are human terms that allow us to assess how things we understand, care about, and can measure relate to each other. Science does not understand, care about, or measure anything, only humans do this.