Tarrasch Variation
French Defense
1.e4 e6 2.d4 d5 3.Nd2 Nf6 4.e5 Nfd7
White avoids the pin on the knight by developing it to d2 instead of c3.
Practice this lineThe idea
White plays 3.Nd2 instead of 3.Nc3, so the knight can't be pinned by ...Bb4 and the c-pawn is free to go to c3 and support d4. After 3...Nf6 4.e5 Nfd7, the position is a closed French where White has a solid, flexible center.
Plans for White
The usual plan is Bd3, c3 and Ne2, keeping d4 well protected, then Nf3 or Nf4 and castling. The bishop on d3 aims at h7, so a kingside attack is often on the cards once Black castles.
Plans for Black
Play ...c5 at once, then ...Nc6 and ...Qb6 to pressure d4. Later, ...f6 attacks e5 and frees Black's position. Black often gets enough activity to make up for White's space.
Watch out for
For Black, the Greek gift. With White's bishop on d3, a knight that can reach g5 and the queen ready to come to h5, the sacrifice Bxh7+ can break open Black's king after castling, especially when Black's knight has been driven away from f6.
For White, trading too much. If d4 is exchanged and White ends up with an isolated pawn, Black's pieces can blockade and attack it.