Semi-Open Game

A Semi-Open Game is a chess opening in which White plays 1.e4 and Black breaks symmetry immediately by replying with a move other than 1...e5. The Semi-Open Games are also called Single King Pawn, Asymmetrical King Pawn, or Half-Open Games, and are the complement of the Open Games or Double King Pawn Games which begin 1.e4 e5.