Figure 2.2.14.4[White to move]

Which Black pieces are loose? Both rooks and the knight. Can White’s queen attack two of them at the same time? Yes, easily via Qd4 or Qc3, winning the knight. Here the queen is just behaving like a bishop; we will see lots of positions like this when we examine bishop forks.

By the way, Black has the option of replying to Qd4 with RxNb1, thus limiting his immediate material loss to the exchange. White replies RxR; Black moves his queen to d8 to guard the knight; and now White has e4-e5, a little fork that wins a pawn. Meanwhile White's b1 rook is now in a much stronger position than before.