This sets how many beacon intervals elapse between Beacon frames whose DTIM Count field is 0, i.e. how often a DTIM (Delivery Traffic Indication Map) beacon is sent, defaulting to 1. Power-saving clients wake specifically for DTIM beacons to check for buffered broadcast/multicast traffic, so an admin raising this value lets clients sleep longer between wake-ups at the cost of slower delivery of that buffered traffic.