Derrière & Échappé

Derrière

At or to the back side. For example, a battement tendu derrière is a battement tendu taken to the rear. Point/face behind you.

Source: Wikipedia

Échappé

Literally "escaped". A movement done from a closed (first or fifth) position to an open (second or fourth) position. There are two kinds of échappés: échappé sauté and échappé sur les pointes or demi-pointes. In an échappé sauté, the dancer takes a deep plié followed by a jump in which the legs "escape" into either second (usually when starting from first position) or fourth position (usually when starting from fifth position), landing in demi-plié. In échappé sur le pointes/demi-pointes the dancer, after taking a deep plié, springs ontopointes or demi-pointes, ending in either second position (when starting from first position) or fourth (when starting from fifth) with knees straight. In all cases, the dancer may or may not return to the initial position, depending on the choreography.

Source: Wikipedia