Bronstein Variation (3...Qd6)

The idea

After 3...Qd6 4.d4 Nf6 5.Nf3 a6, the queen sits on d6, closer to the kingside and harder to hit than on a5. The move ...a6 stops Nb5, which would otherwise attack the queen and c7 together. Lichess names 3...Qd6 the Gubinsky-Melts Defense and this line the Bronstein Variation.

Plans for White

Wikipedia gives White's main setup against 3...Qd6 as d4, Nf3, g3, Bg2, castling and Ne5. The bishop on g2 adds pressure on the long diagonal, and Ne5 or Nb5 ideas can gain time against the queen if Black isn't careful.

Plans for Black

Follow up with ...Bg4 or ...Bf5, ...Nc6 or ...Nbd7, and ...e6 or ...g6. Black often plans ...b5 and ...Bb7 to make use of ...a6. Long regarded as dubious, 3...Qd6 has been shown by many grandmaster games to be quite playable.

Watch out for

For Black, the d6 square. The queen can be hit by Nb5 (if ...a6 is missing), Bf4 or Ne4, so each of White's developing moves may come with tempo.

For White, overpressing. The queen on d6 is not exposed by itself, and chasing it with pawn moves can weaken White's own position.