Dutch Defense: Semi-Leningrad Variation is a chess opening with the ECO code A81, part of the Dutch Defense family. It goes 1. d4 f5 2. g3 Nf6 3. Bg2 g6. White opens with 1. d4 (the queen's pawn) and Black answers 1... f5. After 6 moves it is White to move. The lesson on the board explains every move of the line and lets you play it yourself; it is free.
In chessGM's opening book this position continues with 4. Nf3.
Black answers 1.d4 with 1...f5, grabbing the e4 square. It is ambitious and aims for a kingside attack, but it weakens Black's king a little.
chessGM has a full course for this line: open the Dutch Defense: Semi-Leningrad Variation course lesson.