Technically, the damping factor of a system refers to the ratio of nominal loudspeaker impedance to the total impedance driving it (amplifier and speaker cable). In practice, damping is the ability of the amplifier to control speaker motion once signal has stopped.

What is damping factor?

Damping Factor (DF) is the amplifier's ability to control speaker motion once a signal has stopped.

Is damping factor important amp?

In simplistic terms, it's a measure of the ability of the amplifier to control overshoot, to stop a driver from moving and overcome back EMF. An amp with low output impedance and high damping factor limits this kind of sloppy driver behavior. It's sort of like engine-braking in a car.