802.11a: Ratified in 2002. Operates in five GHz band [where it encounters less interference with cell phones and microwaves] and delivers data rate of about 54 Mbps
802.11g: Ratified in 2003. Fifty-four Mbps in 2.4 GHz band, so backward-compatible with 11b
802.11n: Ratified in 2009. Up to 600 Mbps [in most commercial configurations, about 250 Mbps] in both 2.4 and five GHz frequency bands. A dual-band product that works with 802.11a and 802.11b/g products
802.11ac: Coming to a wi-fi-certified device near you in early 2013. About 1.3 Gbps of data [yes, that's gigabits per second].
"While the Wi-Fi Alliance and the wi-fi industry used to point to these naming conventions a lot, now we just call it wi-fi.
"There are many other 802.11 designations. They refer to a wide array of features that ship in products today—but, thankfully, the industry hasn't burdened users with their names and details.
"Some examples include 802.11i, which underpins the wi-fi security we have today; 802.11e, which includes important mechanisms to support multimedia applications; and 802.11u, which makes up part of the forthcoming Wi-Fi CERTIFIED Passpoint program we are developing, which will make getting on to hot spot networks as seamless as it is with a mobile phone on 3G today."