Flank opening

A flank opening is a chess opening played by White and typified by play on one or both flanks (the portion of the chess board outside the central d and e files). White plays in hypermodern style, attacking the center from the flanks with pieces rather than occupying it with pawns. These openings are played often, and 1.Nf3 and 1.c4 trail only 1.e4 and 1.d4 in popularity as opening moves.

1.Nf3

If White opens with 1.Nf3, the game often becomes one of the d4 openings (closed games or semi-closed games) by a different move order (this is called transposition), but unique openings such as the Réti and King's Indian Attack are also common. The Réti itself is characterized by White playing 1.Nf3, fianchettoing one or both bishops, and not playing an early d4 (which would generally transpose into one of the 1.d4 openings).