Combos are special attack moves that can greatly enhance the damage you are capable of inflicting during combat. Short for combinations, that is exactly what they are – you can combine up to four attack moves into a single combo. You learn combos from a Combo Master.
There are some restrictions on what will work in a combo, however. One obvious fact – you cannot place a Combat Art into a Combo if you have not learned it. If you construct one that does not work correctly, or fizzles, you may need to rebuild it. Below are some links to information about building effective combos.