An opening move in chess begining with White moving his g1 Knight to f3. This is a powerful variant of the King's Indian Attack:
This possition does not become distinct until White fianchettoes both Bishops before challenging the center.
Reti Gambit Accepted
Abandoning the center in this fashion is not recommended. The game scores accumulated from this position give White a strong advantage (17 - 30 percent better for White). Popular lines for White are 3.Qa4+ Nd7 4.g3 transposing into an advantageous variation of the Catalan; 3.e3 Nf6 4.Bxc4 e6 5.d4 (Queen's Gambit Accepted).
With 2...d4 Black commits to a four tempo investment in the center (...d5, ...d4, ...c5, and...e5). Once finished, it will be difficult for White to break through in the center - but countermeasures can be taken immediately. In spite of its overall statistical 'ho-hum,' 3.b4! should give White tactical chances to prevent the creation of Black's massive center.