You can board the Train with wait list ticket ( Only I-Ticket and PRS booked Waitlist ticket) except Duranto , Shatabadi, Rajdhani, Janshatabadi Yuva and Garib Rath trains but can not travel in Reserved Compartment. This rule is very old but not implemented in regular base due to sympathy to WL Passenger. Now IR want to Implement strictly to avoid harassment to confirm passenger in reserved compartments.