Regenerative Braking
Regenerative braking feeds the current produced during braking is back into the power supply system instead of being wasted as heat.
With electrified trains, it is normal practice to incorporate both regenerative and rheostatic braking. If the power supply system is not "receptive", i.e. incapable of absorbing the current, the system will default to rheostatic or pure friction mode in order to provide the braking effect.
In a hybrid-electric vehicle, the electric current is used to recharge the electrical cells (batteries). This allows the energy to be reused later, often in acceleration.
Read more about this topic: Dynamic Braking