Among advocates of voluntary simplicity and related Luddite movements, appropriate technology is technology whose risk/cost/value tradeoff is compelling enough to justify continued use.
The term came into use during the 1973 energy crisis and the environmental movement of the 1970s. A related term, intermediate technology, refers specifically to tools that cost more than those currently in use in a developing nation but much less than those that would be used in a developed nation. This is a first step towards "appropriate" criteria.
It is often used to describe technologies, like wind power, that provide an alternative to fossil fuels. Also, it is sometimes used to describe things like the telephone, radio and television that can reduce the need for travel or replace print. Such usage is controversial, as, very often, windmills or electronics may rely on very high technology elsewhere. It is usually only "appropriate" to use technologies that can at least be locally repaired. Which technologies are truly "appropriate" remains a matter of ongoing debate among those that have pioneered the concept.