A Reservation Against Cancellation (RAC) is a type of ticket that can be sold for travel on the Indian Railways.
[1][2] A berth is split into 2 seats for 2 RAC ticket holders.
The first number shows the status of the ticket at the time of booking.
The second number after the slash (/) shows the current status of the ticket.
So having a RAC ticket means that it is possible to travel without confirmed berth allocation.