"Veela are semi-human magical beings; beautiful women with white-gold hair and skin that appears to shine moon-bright. When angry, Veela take on a less pleasant appearance; their faces elongate into sharp, cruel-beaked bird heads, and long scaly wings burst from their shoulders."
From the Story
Discovered in Book4, Chapter 8, The Quidditch World Cup
"Veela are the official mascots of the Bulgarian National Quidditch team at the Quidditch World Cup. A hundred Veela glide onto the pitch before the start of the match, and start to dance, faster and faster. They have a strange effect upon the men in the stadium; Harry's mind goes completely and blissfully blank as their music begins and he watches them dance, and he feels the urge to do something very impressive, such as jumping from the Top Box into the stadium. When irritated during the match, some of the Veela lose control, launching themselves across the pitch and throwing handfuls of fire at the leprechauns."