CRDI means Common Rail Direct Injection. This term is used in diesel engines.

It is technology for fuel injection which is used in diesel engine.

In this technology fuel is fully controlled by elecronic system called ECU or ECM.

ECU stands for Electronic Control Unit

ECM stands for Electronic Control Module

In this fuel supply system diesel is supplied in a rail from where it is sent to injector as per requirement.

In this rail diesel is always available at high pressure. That's why it is called common rail direct injection.

Hope you understand all concept easily.