Very similar to the dynamic brake, the regenerative brake is a method of retardation that requires either batteries or an external electric power source. It's suitable for electrically powered vehicles of either type.
Like the dynamic brake, it uses the vehicle's motor(s) as generators in order to slow the vehicle down. However, instead of throwing away this electrical energy in a resistor bank in the form of heat like the dynamic brake does, the regenerative brake uses this power, either to charge batteries or to send power back into the external power source, so that it can drive other vehicles also powered from it. A common use is on mountainous railway systems, in which the power generated by a train going downhill helps power another train going uphill.
Regenerative braking is much easier when the external power source is direct current, which is why many early electric railways were DC power.
Modern electric and hybrid cars also use regenerative braking to recharge the on-board batteries. This is part of how they can achieve greater distances and better economy.