Someone whose diet consists of food grown or produced within an area most commonly bound by a 100-mile radius of their home. Locavores usually shun large supermarket chains, opting for farmer's markets and local gardens instead. It is also a current trend for many high-end restaurants as well.
Interesting tidbit — this word was just declared Oxford American Dictionary's 2007 Word of the Year. It was coined in 2005 by a group of four women from San Francisco.
It's also sometimes spelled localvores.