don't really think there's a particular term for it, it's just a partial overspin.
when the cutoff lever trips, and assuming there's no active braking from a mosfet, the motor just shuts off but the mass of the rotating parts, the gears etc are still spinning so they just keep rolling until something stops them, which will be a combination of natural friction, the strength of the magnets in the motor (eg a strong neodynium motor will slow down quicker) and, when it hits the piston again, the energy to pull back the spring.
overspin usually isn't commented on unless you have a fast enough setup that it can not only pull the piston back a little, but all the way to roll over to a second shot (which is the double tap). as mentioned it's the same effect as you're intentionally trying to acheive if you're using a mosfet with precocking, which will run the motor intentionally a little longer so when it stops it's nearly all the way back, idea being the time between pulling the trigger and the shot actually firing is much shorter without the need to have a really fast motor/gear combo.
it's genuinely nothing to worry about, indeed depending on the setup you actually want it to happen a little bit, as if you stopped the motor too quickly (eg by using active brake) then it can stop quick enough to have the cutoff lever still engaged and lockup the trigger.