Wi-Fi (pronounced /ˈwaɪfaɪ/) is a trademark of the Wi-Fi Alliance for certified products based on the IEEE 802.11 standards. This certification warrants interoperability between different wireless devices.
In some countries the term Wi-Fi is often used by the public as a synonym for wireless LAN (WLAN); but not every wireless LAN product has a Wi-Fi certification, which may be because of certification costs that must be paid for each certified device type.
Wi-Fi is supported by most personal computer operating systems, many game consoles, laptops, smartphones, printers, and other peripherals.
more - http://en.wikipedia.org/wiki/Wi-Fi

A wireless LAN (WLAN) is a wireless local area network that links two or more computers or devices using spread-spectrum or OFDM modulation technology based to enable communication between devices in a limited area. This gives users the mobility to move around within a broad coverage area and still be connected to the network.
For the home user, wireless has become popular due to ease of installation, and locatis with on freedom with the gaining popularity of laptops. Public businesses such as coffee shops or malls have begun to offer wireless access to their customers; some are even provided as a free service. Large wireless network projects are being put up in many major cities: New York City, for instance, has begun a pilot program to cover all five boroughs of the city with wireless Internet access
more - http://en.wikipedia.org/wiki/Wireless_LAN