Wi-Fi means "Wireless Fidelity".It is the popular term for a high frequency Wireless Local Area Network (WLAN)that is generically referred to as 802.11 network,more specifically the 802.11b nomenclature given by the Institute of Electrical and Electronics Engineers(IEEE).It is a part of a series of wireless specifications developed by IEEE.
WLAN is fast evolving and provides benefits in terms of speed,security,quality of service(QoS) and cost.It scores over wired LAN with mobility and ease to setup.Products marked "Wi-Fi certified"(a registered trademark)by Wi-Fi alliance are interoperable with each other,even if they are from different manufacturers.

Wi-Fi Facts:

802.11 refers to a family of specifications developed by IEEE for wireless LAN.The several wireless specifications are mentioned below:

1)802.11:Applies to wireless LANs and provides 1 or 2 Mbps transmissions in the 2.4GHz band either frequency-hopped spread Spectrum(FHSS) or direct-sequence spread spectrum(DSSS).

2)802.11a:An extension to 802.11 that applies to wireless LANs and works on 5GHz frequency spectrum at maximum data transfer rate of 54Mbps.

3)802.11b:Also referred to as 802.11 high rate or Wi-Fi,it is an extension to 802.11 that applies to wireless LANs and provides 11Mbps transmission (with fallback to 5.5,1 and 1 Mbps) in the 2.4GHz band.

4)802.11g:Offers wireless transmissions over relatively short distances at up to 54Mbps and operates in the 2.4GHz range.

As an Indian I would like to share my knowledge in INDIA.In India ,only 802.11b standard working on 2.4GHz frequency range has been delicensed for indoor use.Hence this is the most popular standard currently.The 5GHz spectrum has not been delicensed for se since it coincides with the spectrum used by the police department.