The [fianchetto][1] is a term for the development of a bishop to the second rank of the adjacent knight's file, after having moved the knight's pawn one or two spaces. The main idea behind such a development of the bishop is that it is placed on one of the longest diagonals on the board, potentially increasing its scope/activity, and it can increase central control by surveying two key squares (either e4 and d5, or d4 and e5).


  [1]: https://en.wikipedia.org/wiki/Fianchetto