The difference between single-deck and multi-deck blackjack games primarily lies in the number of decks used, which affects game dynamics and strategy. Single-deck games use only one deck of cards, making it easier for players to track cards and potentially gain an advantage through counting. They typically offer better odds for the player, as the likelihood of certain card combinations occurring is higher. In contrast, multi-deck games, which can use anywhere from two to eight decks, increase the house edge and make card counting more challenging.