Pirc Defense is a chess opening with the ECO code B00. It goes 1. e4 d6 2. d4. White opens with 1. e4 (the king's pawn) and Black answers 1... d6. After 3 moves it is Black 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 2... Nf6.
Black answers 1.e4 with 1...d6, then ...Nf6, ...g6 and ...Bg7. Black lets White build a centre and counterattacks it later.
chessGM has a full course for this line: open the Pirc Defense course lesson.