How many beacon intervals the station may sleep through before it wakes to check for buffered traffic.
The one number in this frame that costs the AP something. A large value means longer battery life for the station and more buffering for the AP, and an AP may refuse the association if it cannot honour it. Multiply by the Beacon Interval to get real time — and remember a time unit is 1024 microseconds, not a millisecond.
Association Request MPDU > Frame Body > Listen Interval