Caro-Kann Defense
An opening against 1.e4 for black. Low-theory, positional opening. Famously taught by the well-known chess youtuber GothamChess. It is used at the top-level because of how risk-free this opening is. Also, it has less theory to memorize for black compared to the other main openings against 1.e4. I highly recommend this to players who are a fan of the carlsbad pawn structure, and like slow games.
Image credit: Caro-Kann