Loosely, WiMax is a standardized wireless version of Ethernet intended primarily as an alternative to wire technologies (such as cable modems, DSL, and T1/E1 links) to provide broadband access to customer premises. This application is often called wireless last/first-mile broadband because the transmission distances involved are typically of this order and the engineering problem is to bridge the final gap between the customer premises and the telco’s or service provider’s main network. The technology is specified by the Institute of Electrical and Electronics Engineers Inc. (IEEE), as the IEEE 802.16 standard.
More strictly, WiMax is the Worldwide Microwave Interoperability Forum, a non-profit industry body dedicated to promoting the adoption of this technology and ensuring that different vendors’ products will interoperate. WiMax will do this through developing conformance and interoperability test plans, selecting certification laboratories, and hosting interoperability events for 802.16 equipment vendors. But WiMax is such a convenient term that people tend to use it for the 802.16 standard and technology themselves, although strictly it applies only to systems that meet specific conformance criteria laid down by the WiMax Forum.
The 802.16 standard is large, complicated, and evolving, and offers many options and extensions, so interoperability is a major issue that must be addressed. In particular, one extension known as 802.16a became the focus of a lot of industry attention because it should be the easiest and most useful to implement. So it is likely that when people talk loosely of WiMax they are referring to the technology for fixed wireless specified by 802.16a and its later version 802.16d.
802.16 is one of a family of technologies being standardized by the IEEE (with other bodies, such as the European Telecommunications Standards Institute (ETSI), whose Hiperman standard is harmonized with 802.16) to create wireless versions of Ethernet that can operate over distances from a few meters to tens of kilometers -- from personal area networks (PANs), through local area networks (LANs) and metropolitan area networks (MANs), to wide area networks (WANs). 802.16 is the MANs member of the family.