What is PNR number?
A unique code is given to every passenger who has booked their tickets in all the classes. It's a ten digit number which stores all the information of passengers such as Passenger name, boarding details, train number, train name, ticket status, etc.
The number is generated depending upon the zone and station from which you're traveling. All the details will be stored on the server and can be requested by knowing the ten digit number.
Why is it necessary?
Passenger name record number is necessary to check the status of the ticket if it's in waitlist or RAC category. Reservation of seat has been implemented by railways long back to avoid chaos between the passengers. So the railway CRS started this function to generate unique numbers to every ticket.
If a passenger has his ticket in waitlist or in RAC category then he can know the status of his seat regularly in the runningtrain website or the official Indian railway's website before the final preparation chart is made.
How to check the PNR status?
There are mainly three chances that your ticket will appear after booking in waitlist.
CNF: This means that the ticket is confirmed and the passenger will get a berth or seat to travel without sharing with anyone.
WL: This means that the ticket is still in waitlist and waiting for spaces available in the moving train.
RAC: This means Reservation against cancellation. RAC is usually given when the number of people has their ticket in waitlist mode. Here the berth is shared by two members.
Indian railways notified that waitlist tickets will be canceled automatically after the final chart preparation is made and the money will be refunded when booked online. In such cases, if the ticket is in RAC mode then the ticket will not be canceled and if the passenger is willing to share a seat with another during the journey then he can continue with the ticket.
If you don't get the information about your waitlist ticket then there are few possibilities to look for.