In the Drawn to Life series, a Combo is when The Hero strings together a lot of attacks within a short space of time.
Drawn to Life
In Drawn to Life, the combo is signaled by its name coming up on the screen after it has ended. Whilst it is ongoing, the number can be seen each time it is increased by another hit on an enemy and is signaled by a number with a multiplication sign next to it (e.g. x5). Combos produce a reward: money. With a greater-value Rapo-Coin, the higher the combo number is.
Types of Combos
Nice combo: 5+, a 
for every hit 2+
Great combo: 10+, a 
for every hit 10+
Super Combo: 15+, a 
for every hit 15+
Drawn to Life: The Next Chapter
In Drawn to Life: The Next Chapter, the combo is signaled by its name coming up on the screen after it has ended. This is just like in its prequel. The number can be seen whilst the combo is still going, with the new number appearing each time another hit on the enemy occurs, just like in the first game. In The Next Chapter, the combos begin at a lower number, and there is one more present than in the original game. This makes it easier to get combos as well as the rewards that come with them. The combos in this game also produce Color Drops along with Rapo-Coins.
Types of Combos
Nice combo: 3+
Great combo: 5+
Super Combo: 7+
Insane Combo: 10+