What is "coup de glotte"

Coup de glotte or 'shock of the glottis' is a term used in the theory of singing technique to describe a particular method of emitting or opening a note by an abrupt physical mechanism of the glottis (the space between the vocal folds). During the 19th century there was disagreement among teachers and performers as to whether the technique should be taught as a normal part of vocal method or not. The technique is still sometimes used to achieve particular effects, dramatic or ornamental, but is usually avoided in the teaching of fundamental vocal method.