Nomenclature
Various terms in 802.11 are used to specify aspects of wireless local-area networking operation, and may be unfamiliar to some readers.
For example, Time Unit (usually abbreviated TU) is used to indicate a unit of time equal to 1024 microseconds. Numerous time constants are defined in terms of TU (rather than the nearly equal millisecond).
Also the term "Portal" is used to describe an entity that is similar to an 802.1H bridge. A Portal provides access to the WLAN by non-802.11 LAN STAs.
Read more about this topic: IEEE 802.11