"Like American jazz, flamenco dancing involves improvisation. Its the dancer’s spontaneous expression of the moment’s emotions. The Spanish call it duende (DWEN-day). The word means goblin or fairy, but to the flamenco dancer it signifies an inner force that fuels an inspired performance.
A dancer with duende goes beyond technical mastery to vent his or her feelings, achieving a powerful, compelling dance. Those who aren’t singing may shout encouragement: olé or ¡baile! ¡baile! — dance! dance! As an observer, you don’t really see good flamenco, you feel it."
Thanks to Alexis Givens for the powerful description. No one could have said it better.