When a Piece or Pawn is in a situation to be taken by the enemy, it is said to be en prise. To put a piece en prise, is to play it so that it may be captured.
Howard StauntonThe Pawn moves only one square at a time, and that straight forward, except in the act of capturing, when it takes one step diagonally to the right or left file on to the square occupied by the man taken, and continues on that file until it captures another man.
Howard Staunton