PQWL is one of the many Waiting List types that appear on reservation tickets. Practically speaking this is a Waiting List. Technically, there's a difference between PQWL, CKWL, GNWL etc. The total seats available for reservation on a train are divided among different quotas. There's the ladies quota, tatkal quota and general quota. Some trains also have what is called the Pooled Quota or PQ. When you book a ticket to a station for which tickets are issued from the pooled quota, then you get a pooled quota waiting list or PQWL if all the tickets available in the PQ quota have already been booked. This is similar to CKWL (Waiting list on the tatkal quota). The pooled quota is used for a bunch of stations who share a pool of tickets. These are relatively minor stations, at least as far as that particular train is concerned. For eg. if you were to book a ticket from Bangalore(SBC) to Rajamundry(RJY) on the Guwahati Express (2509), then you would get tickets assigned from the Pooled Quota. Waiting lists from this PQ quota appear as PQWL on the ticket.