Electronic Reservation Slip (ERS) - The printout in standard specified Performa containing reservation particulars, and instructions for use which can be used by the passenger along with the relevant authorized Identification, as travel authority for performing the journey.
 
Virtual Reservation Message (VRM) - A screen-shot of the e-ticket displayed through laptops/palmtops/ Mobile phone is referred as Virtual Reservation Message (VRM).
 
ERS/VRM/SMS sent by IRCTC along with any one of the nine prescribed ID proofs in original and the indication of the passenger(s)' name(s) in the Reservation Chart will authorize the passenger to travel
 
VRM/ SMS sent by IRCTC combined with valid photo-id in original will be treated as an instrument on par with the ERS.
 
ERS/VRM/SMS sent by IRCTC along with one of the nine prescribed proofs of identity in original will also authorize the passenger to enter the platform on the day of journey and he/she will not be required to purchase platform ticket. ERS/VRM/SMS sent by IRCTC along with original id proof will be required to be produced on demand of Ticket Checking Staff on the platform.
 
Reference :
1) Railway Board Letter No.2008/TG-I/10/P/SMS dated 20.07.2011
 
2) Railway Board Letter No.2008/TG-I/10/P/SMS dated 01.02.2012