When electrons move back and forth, reversing their direction regularly, the current is called?

It is called "alternating current" or "ac current".

An alternating current is a current the periodically changes direction. Basically, the voltage difference applied at the two ends of the wire / of the circuit is constantly reversed. This means that at some point electrons travel in one direction, then the voltage is switched (i.e. the polarities are exchanged) and the electrons start to flow into the opposite direction, and so on.