In chess, the fianchetto, ‘little flank’ in Italian, is a pattern of development wherein a bishop is developed to the second rank of the adjacent knight file, the knight pawn having been moved one or two squares forward.
The fianchetto is a staple of many hypermodern openings, whose philosophy is to delay direct occupation of the centre with the plan of undermining and destroying the opponent’s central outpost.
One of the major benefits of the fianchetto is that it often allows the fianchettoed bishop to become more active. Because the bishop is placed on a long diagonal, it controls a lot of squares and can become a powerful offensive weapon.
However, a fianchettoed position also presents some opportunities for the opposing player: if the fianchettoed bishop can be exchanged, the squares the bishop was formerly protecting will become weak and can form the basis of an attack. Therefore, exchanging the fianchettoed bishop should not be done lightly, especially if the enemy bishop of the same colour is still on the board.
‘Strictly speaking, fianchetto is a noun – a diminutive of an Italian word meaning wing or flank – but the English have long misused it as a verb. The true pedant, however, will always refer to a ‘bishop in fianchetto’, and never a ‘fianchettoed bishop’.’
– Hartston. B. 1997. Better Chess London, United Kingdom: Hodder Headline (2004) p. 26