Chess Opening Theory/1. e4/1...c6/2. d4/2...d5/3. e5/3...c5

This is Black's second most common option, after 3...Bf5. It is an attack on the base of White's pawn chain.

After 4. dxc5, Black can eventually recover the pawn with ...e6 and ...Bxc5, though there is usually no hurry and it's not in White's best interests to hold onto the c-pawn too tightly. One line is 4...Nc6 (the e5-pawn is now loose) 5. f4 e6 6. Be3 d4 7. Bf2 Bxc5⩲.

4. Nf3 allows 4...cxd4 and prepares to recapture the pawn with the knight. 5. Nxd4 Nc6 (e5 is loose) 6. Nxc6 bxc6 7. Bd3 prevents Black from developing their light-square bishop actively.

4. c3, preparing to recapture on d4 with a pawn, is a minor sideline but very common in amateur play. Black does not need to take d4 straight away: they can leave the tension and focus on development.

This line is named after World Champion Mikhail Botvinnik and Carl Carls.

Carls had one of the earliest appearances of the line in Breslau, 1912.^[1] However the line remained uncommon until Botvinnik relied upon it in his 1961 rematch with Mikhail Tal.^[2][3][4] Botvinnik won the match and regained the World Championship title.

Wikipedia has related information at Caro-Kann.