रेलफैनों को आता है ज़िन्दगी का मज़ा लेना

When reservation starts all seats are available.. as reservations continue to happen, seats get filled.
When all confirmed seats are filled, 2 passengers each are assigned to RAC seats. Both passengers can travel by sharing the berth.
When all RAC seats are filled with 2 passengers each, then all subsequent reservations go into Waitlist since there is no berth available to allot to them. This is what happened to your reservation when you booked it.
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more people ahead of you cancel their tickets, you will move up in the queue and first reach RAC status (which you have reached now) and if enough number of people cancel even more reservations then you will eventually reach Confirmed status.
In addition, if some additional unutilised berths from other reserved quotas are released at chart preparation time then also you might have a chance to jump from RAC to Confirmed status.