A Reservation Against Cancellation (RAC) is a type of ticket that can be purchased for travel on the Indian Railways. Although it ensures certainty of travel, it does not guarantee a berth. A berth will be allocated to the person who reserves an RAC ticket if passengers who already have a confirmed ticket do not turn up before the train departure or get their confirmed ticket cancelled. A berth is split into 2 seats for 2 RAC ticket holders. If there’s any last minute cancellations, or if any quota allocations remain unsold, or if any confirmed ticket holders are given a free upgrade (more later), an RAC ticket holder is given the empty berth, the other RAC ticket holder can then convert the 2 seats into a berth.
Generally, RAC/WL tickets will have two numbers - RAC8/RAC2, WL20/W15, WL12/RAC2, etc. The first number shows the ticket status had nobody cancelled any ticket after the first unconfirmed ticket was sold for that train on that journey date. The second number after the slash (/) shows the status of your ticket at the time of booking. So, RAC8/RAC2 means that when you purchased the ticket, yours was the 2nd such ticket under RAC category, although as per the initial unconfirmed ticket selling status, your position was 8th, which has moved 6 places after 6 cancellations before your position. You can check out the current status of your booking by entering 10-digit PNR number at PNR Status.