Different types of Waiting Lists: 1) RLWL - Remote location waiting list 2) RLGN - Remote location general waiting list 3) RQWL - Request waiting list 4) PQWL - Pooled quota waiting list 5) LDWL - Ladies quota waiting list 6) GNWL - General waiting list 7) CKWL - Tatkal quota waiting list
An update: TQWL (known as CKWL) - This code is used for the tatkal tickets. It was changed from CKWL by the Indian Railways from December 2016.