Tying these together makes for a combo. Simply scoring two or more hits in a row due to a couple of moves or mashing pokes are things that are difficult to call a combo. Sometimes, the term “2-in-1” is used to denote a simple transition from a normal move into a special move (often through a cancel; the term is used because getting both to succeed is almost as easy as getting one to succeed, hence two for the price of “one”).
In most games, the number of hits will be counted and displayed. This first began with Street Fighter II, where the numbers would only be displayed after the sequence finished (in many non-Capcom games, the number tends to be shown on the screen as it happens).
The key point to remember about sequential hits is that the opponent (in normal circumstances) cannot do anything to escape in between them. This is why combos are so important.