RAC stands for Reservation Against Cancellation, which is a type of ticket that can be sold for travel on the Indian Railways. An RAC ticket allows a passenger to travel in a train but does not guarantee a berth. A berth will be allocated to the ticket holder who reserves an RAC ticket if passengers who already have a confirmed ticket do not board before the train departure or get their confirmed ticket cancelled. A berth is split into 2 seats for 2 RAC ticket holders. An RAC ticket holder is given an empty berth if there are any last-minute cancellations, if any quota remains unsold, or if any confirmed ticket holders are given a free upgrade according to seat availability in upper class. If this happens, the other RAC ticket holder can then convert the 2 seats into a berth. Generally, RAC/WL tickets will have two numbers - the first number shows the status of the ticket at the time of booking, and the second number after the slash (/) shows the current status of the ticket. So, RAC8/RAC2 means that when the ticket is purchased, it was the 8th such ticket under RAC category, which has moved 6 places after 6 cancellations. It can be assumed that it was the 8th ticket in the queue and is now the 2nd.

In summary, RAC seat in a train means that the ticket holder is allowed to travel in the train but does not have a confirmed berth. The ticket holder may be assigned a berth if there are any last-minute cancellations or if any confirmed ticket holders are given a free upgrade according to seat availability in upper class.