Wiktionary
semi-closed game
n. A chess game in which the queen's pawn advances two spaces in the first ply move, but not in the second ply move.
Wikipedia
Semi-Closed Game
A Semi-Closed Game (or Semi-Closed Opening) is a chess opening in which White plays 1.d4 but Black does not make the symmetrical reply 1...d5. (The openings starting 1.d4 d5 are the Closed Games.)