It is an alternate picking technique used for soloing in Flamenco. The index and middle fingers are used alternately. The thumb is placed on the low E string when the higher strings are played, and the fingers land on the string above. This technique produces a stronger sound. Starting from the D string and higher, the hand needs to be raised so that the thumb is no longer resting on the E string. Classical guitarists typically use a free-stroke when they solo, which results in a softer sound.