Definition of combo
The word combo is short for combination in English. Depending on the discipline in which it is used, combo will have a multitude of meanings. In poker, we will use the word combo to define two particular things. First, combo will define possible combinations in our opponent's range. If we take a hand like AK, we can form 16 different combos using all 8 cards (AK of hearts, AK of spades, A of spades K of clubs, etc). These 16 combos represent 16 out of 1326 possible combos (when you receive 2 random cards in Hold'em, you will receive one of the 1326 possible combos...). At a certain stage of a hand, you may ask yourself "Does Naughty have AK combos in his range since he doesn't have 3bet preflop"?
The combo draws
If you play Omaha, you will often hear the term "combo draw". The term is also used in Hold'em, but is more common in Omaha. If you have a hand like KQ in spades on J-T-2 with two spades, you are said to have a "combo draw," which is a hand that will give you a multitude of outs. By combo, we mean any turn + river combination that could come to your aid. Here, any 9, A or spade would help you. Perhaps even a K or Q could help you.