Wi-Fi is short for wireless fidelity -- used generically when referring of any type of 802.11 network, including 802.11b, 802.11a, and 802.11g. It is a trade term promulgated by the Wireless Ethernet Compatibility Alliance (WECA). "Wi-Fi" is used in place of 802.11 in the same way that "Ethernet" is used in place of IEEE 802.3. Products certified as Wi-Fi by WECA are interoperable with each other even if they are from different manufacturers. A user with a Wi-Fi product can use any brand of Access Point (AP) with any other brand of client hardware that is built to the Wi-Fi standard.

Google definitions of Wi-Fi, Access Point (AP), hacker, freeware, SSID (Service Set Identifiers), MAC address, WLAN (Wireless Local Area Network), WEP, authentication, encryption, Denial of Service (DoS) attack.

Wi-Fi Marketplace:
HyperLink Technologies for a wide variety of useful Wi-Fi accessories.

AirDefense.net recently published a White Paper which included the following Freeware software products available to hackers and white hat security researchers:
NetStumbler for freeware wireless access point identifier - listens for SSIDs and sends beacons as probes searching for access points.
Kismet for freeware wireless sniffer and monitor - passively monitors wireless traffic and sorts data to identify SSIDs, MAC addresses, channels and connection speeds.
Wellenreiter for freeware WLAN discovery tool - uses brute force to identify low traffic access points; hides your real MAC address; integrates with GPS.
THC-RUT for freeware WLAN discovery tool - uses brute force to identify low traffic access points. "Your first knife on a foreign network."
Ethereal for freeware WLAN analyzer - interactively browse the capture data, viewing summary and detail information for all observed wireless traffic.
WEPCrack for freeware encryption breaker - cracks 802.11 WEP encryption keys using the latest discovered weakness of RC4 key scheduling.
AirSnort for freeware encryption breaker - passively monitoring transmissions, computing the encryption key when enough packets have been gathered.
HostAP for conversion of a WLAN station to function as an access point. (Available for WLAN cards based on Intersil's Prism2/2.5/3 chip set)
WEPWedgie for toolkit that determines 802.11 WEP keystreams and injects traffic with known keystreams in order to crack WEP in minutes.
AirSnarf for soft AP setup utility that steals user names and passwords from public wireless hotspots by confusing users with DNS and HTTP redirects from a competing AP.
SMAC for Windows © MAC Address modifying utility which allows users to change MAC address network interface cards (NICs) on Windows 2000, XP and 2003 Server systems, regardless of whether the NIC manufacturer allows this or not.