A fianchetto is the development of a bishop to b2 or g2 (for White) or b7 or g7 (for Black), preceded by advancing the pawn to b3/g3 (or b6/g6), placing the bishop on the long diagonal to control the center from the flank.
This structure creates a natural shelter for the king after castling, as the fianchettoed bishop guards the squares in front of the king. It is one of the most common ideas in modern openings and appears in systems such as the Sicilian Dragon, the Réti Opening, and the Indian Defenses.
In practice, the fianchetto takes two moves to set up, but rewards you with a bishop that radiates across the entire diagonal and actively influences the center. Once you have castled, your king gains solid cover. Be careful, however, not to trade this bishop away without good reason: its absence leaves several weakened squares around your king that an opponent can quickly exploit.
