802.11 -- applies to wireless LANs and provides 1 or 2 Mbps transmission in the 2.4 GHz band using either frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS).
802.11a -- an extension to 802.11 that applies to wireless LANs and provides up to 54 Mbps in the 5GHz band. 802.11a uses an orthogonal frequency division multiplexing encoding scheme rather than FHSS or DSSS.
802.11b (also referred to as 802.11 High Rate or Wi-Fi) -- an extension to 802.11 that applies to wireless LANS and provides 11 Mbps transmission (with a fallback to 5.5, 2 and 1 Mbps) in the 2.4 GHz band. 802.11b uses only DSSS. 802.11b was a 1999 ratification to the original 802.11 standard, allowing wireless functionality comparable to Ethernet.
802.11g -- applies to wireless LANs and provides 54 Mbps in the 2.4 GHz band (backwards compatible with 802.11b).
802.11n (MIMO)- Multiple In Multiple Out, multiple transmitters, higher speeds, spectrum still under review. 300+ mbps ?
802.11ac, 7Gbps, 5Ghz, 8 8 Channels
802.11ad WiGig, 7Gbps, 2.4/5/60Ghz, 4 Channels