What is Sideline in chess?
A less common opening variation that deviates from the most popular main line.
Sidelines can be perfectly playable - sometimes they are chosen deliberately to avoid heavy theory. However, they are generally considered less critical than main lines and may offer fewer winning chances.
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Analyze my games →More chess terms
- Development leadHaving more pieces developed (off the back rank) than the opponent.
- En passantA special pawn capture of a pawn that just advanced two squares.
- CastlingA move that tucks your king to safety and activates a rook.
- Kingside castlingCastling toward the h-file, also written O-O, moving the king to g1 (or g8).
- Queenside castlingCastling toward the a-file, also written O-O-O, moving the king to c1 (or c8).
- Promotion (queening)A pawn reaching the far rank becomes any piece, almost always a queen.