Think of a train which has 100 reserved seats and 10 seats r for the RAC pax in that train. Now if already 110 people has reserved in that train and u r the 111th person to reserved in that train, then ur ticket will be in waiting list. Now suppose 1personout of those 110 before u has cancelled his ticket, then u ticket moves one position forward and u come within the 10 person who will have a RAC ticket. So u will now get a RAC ticket. Now suppose again 10 people out of those 109 peoples before u cancel their ticket in that train, so now u move forward by 10position and now u r among the 100 pax who will get a confirm seat.so now u will get a confirm ticket. If those cancellations don't occur then ur ticket will remain in RAC or WL as per...
more... the availability.
The sequence of getting confirm ticket in a train with WL is
WL>>RAC>>confirm