"WLAN - is the acronym for Wireless Local Area Network and is also called WiFi in marketing language. It is based on a family of standards by the IEEE which all start with the numbers 802.11 (a, b, c, etc.). The technology operates in a band of the electromagnetic spectrum which according to international conventions has been made licence exempt, which means that everybody can use it without having to ask for permission first. One of the licence exempt spectrum bands is at and above 2.4 GHz."
"The WLAN standard 802.11b has two modes, the infrastructural mode (for Access Points) and the ad-hoc mode (also called peer-to-peer or computer-to-computer mode, depending on hardware/software vendor). When a wireless network is set-up in the latter way, each node can connect to each other node as long as they are within range of their radio signals. Since there is no privileged place in the network, each node carries out functions of switching data packets around, acting as a router and Internet gateway. Since every node shares this task of switching packets around, the overlapping radio coverage of all nodes together forms a single wireless cloud." (http://theoriebild.ung.at/view/Main/WirelessUtopia)
See how it is used by the Free Networks Movement