What is flamenco guitar?

Flamenco guitar has always been in a process of revolution.  Guitar was first used in flamenco at least 200 years ago to accompany the cante (singing).  Little is known of what the earliest playing styles were like, given the absence of written music (flamenco guitar, like the cante, has always been an oral tradition and even today written music is rarely used), although it probably comprised of various strumming techniques using mostly the thumb and index fingers of the right hand.  In the second half of the nineteenth century guitarists started to combine techniques borrowed from classical guitar with existing flamenco techniques.  Since then the music has been further redefined by guitarists such as Ramon Montoya, who introduced many new ideas and was instrumental in creating a solo playing style, and Paco de Lucía, who radically expanded flamenco's harmonic and melodic vocabulary by bringing in influences of other musical traditions, especially jazz.  This has opened up a new world for the next generation of guitarists, such as Vicente Amigo, Tomatito and Gerardo Nuñez, who continue to redefine flamenco guitar.

What is flamenco?
How do I learn to play flamenco guitar?