RAC - Reservation Against Cancellation
A Reservation Against Cancellation is a type of ticket that can be given to a passenger traveling through Indian Railway. Unlike a Waiting Ticket, an RAC ticket can get you on train but it does not guarantee a berth. There’s a chance that you could end up with just a seat.
Usually, for Reservation Against Cancellation, a birth (Usually a side birth) is split into two separate seats, which can be allotted to a passenger of RAC ticket. The RAC holders may also get an empty birth if some cancellations have been done.
In Indian Railway, Reservation Against Cancellation tickets can be allotted only for 2nd AC, 3rd AC, Non-AC 1st Class and Sleep Class only. RAC tickets can only be sold, when there are no more tickets available in a particular class.