What is RAC?
A Reservation Against Cancellation (RAC) is technically a train ticket with confirmed seat but wait listed berth.
I
n other words, if your train ticket shows RAC as its status (with an RAC status number), you can board the train and occupy the seat allowed, instead of a sleeping berth at night.In fact the seat you are allocated is a shorter version berth, shared by one more RAC status co-passenger. You still are wait listed for a berth throughout the journey. If any berth is available during the journey, the conductor (TTE) allocates it to you based on your ticket's RAC position.
Yes, RAC & WL are a bit complicated concept in the Indian trains. But this is a very useful process in the Indian Trains systems to give a better chance for the wait listed (WL) passengers.