Combos are any group of cards played at the same time. When you play combos, ignore the instructions on the cards and do the following instead:
Two of a kind
Playing Pairs (where you get to steal a random card from another player) no longer only applies to cards with no instructions on them, it now applies to any cards in the deck with the same icon in their corners.
Three of a kind
Exactly the same as Two of a Kind, but you get to name the card you want from the other player. If they have it, you get to take it. If not, you get nothing.
5 different cards
If you play any 5 cards that have different icons in the corners (with instructions, without instructions, or any combination), go through the Discard Pile to take any single card you'd like. (Grab the Pile quickly to choose your card so that you don't get "Noped!")