RAC: Reservation Against Cancellation.
In above Picture you can see after chart preparation they got reservation in RAC mode.
R= Got confirmed sharing seat after chart preparation.
The main Benefits of RAC Confirm passenger is
1) After Chart you got RAC Seat and if you don’t want travel, you can cancel tickets and you will be got refund same as Waiting list cancellation.
2) In this mode you are authorized to travel in reservation coach specially benefit for fully waiting list e-tickets passenger.
S11 71= The Same as Confirmed tickets. The Only difference is on the 71 number berth which is half allotted to you and Half allotted another person who have also RAC Confirm.
Still Any confusion Just put in comments.
Note: Your ticket is 100% confirmed now. In peak season Railways adds additional sleeper coaches in trains which are known as RS.
Note: If you canceling a RAC ticket, it is treated just like a W/L ticket and you will almost get the same (full) refund as when you cancel a W/L ticket.