This refers to the wireless transmission standards IEEE 802.11a and IEEE 802.11g. There is also an IEEE 802.11b and IEEE 802.11n just to confuse you more.
The IEEE is the Institute of Electic and Electronic Engineers and is the body responsible for setting many of the standards used by computers and electrical components. This allows different manufacturers to produce equipments that will work with those manufactured by others.
802.11a equipment uses a different frequency band (5Ghz) than 802.11g which uses 2.4Ghz.
Hope this helps.