Ah, easy to get terms confused. Every deck worth its salt has what you might call combos, but usually that means just interacting cards with some kind of synergy. That's a basic tenet of the game. A combo deck however takes this a step further. It relies on several, usually complex and not immediately obvious interactions to shut down the opponent and win the game, ideally all in one go so the opponent has little chance to react. Those combos usually involve several cards to work, but when you do get it to work it often means game over straight up.