A particular kind of music/dance (and some would say lifestyle) native to, but no longer restricted to, a small region of Andalucia in Southern Spain. Like American "blues" it probably has ancient antecedents, but as a distinct genre is only a couple centuries old. Not all Andalucian folk music is flamenco. Not all flamenco artists have been Andalucians (eg Sabicas), or even Spanish (eg Greco).

Flamencos themselves (ie guitarists, dancers, singers, aficionados), whatever their own specialty, and for both formal and historical reasons, usually agree that what is fundamental to flamenco is cante (song), i.e. a body of several dozen forms (palos) with specific rhythms, melodies, and in some cases themes, sung in a certain way.

Flamenco guitar started as accompaniment for cante, and in Spain has largely remained that, no matter how technically refined it has become. Probably the same is true of flamenco dance -- that it started as an embellishment through movement of what the singer was doing. Even the virtuosos like Paco de Lucia and the late Sabicas who are famous for solo work (and who play other music besides flamenco) would probably define flamenco in terms of cante rather than of guitar technique. Both started within the tradition as accompanists of cante, and were superb ones. To anyone familiar with cante, even their solos imply the cante from which they came.