Slav Defense: Exchange Variation is a chess opening with the ECO code D10, part of the Slav Defense family. It goes 1. d4 d5 2. c4 c6 3. cxd5. White opens with 1. d4 (the queen's pawn) and Black answers 1... d5. After 5 moves it is Black to move. After the last move White is a pawn ahead in material. 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 3... cxd5.
After 1.d4 d5 2.c4, Black defends d5 with 2...c6. Unlike the QGD, the light-squared bishop can come out to f5 or g4.
chessGM has a full course for this line: open the Slav Defense: Exchange Variation course lesson.