Here is a run down of the different types of combos and infinites, I'll use UMK3 for examples.
A combo is 2 or more consecutive hits that cannot be broken once started, but ends based on character properties, even if the 2 hits are performed by one attack. Examples: aaHPHP = 2 unbreakable hits, and Jax's F,F, LP always does 2 hits but is one special move.
An infinite is a when you perform an attack, special move, or a series of attacks and/or special moves infinitely that can never be broken by character properties or game physics. Example: Kung Lao's corner spin -> straight up JK is a true infinite.
A semi-infinite is similar to an infinite where there is a pattern to the hits, except it can be broken by game physics such as built in universal limitations like walls or damage limits, and not necessarily character/move properties. Example: relaunch combos are semi infinites because they must stop when they hit the wall.
A 100% (or more) combo is when a series of hits that doesn't have a pattern happens to do 100% damage or more but doesn't have the properties of an infinite. Example: Ermac's corner 100% combos, while some may appear to have patterns, cannot be performed infinitely if damage is turned off.
A time infinite is a series of hits that either doesn't, or eventually doesn't do damage and can be performed until the round is over, but never do 100%. Example: In MKT Rain can perform multiple Rain Balls under the opponent as they are in there. For some reason it leaves them stuck there if you perform then the instant he recovers.
Reptile's, aaHPHP->dash whiff is a potential 100% combo because you are performing a repeating pattern of hits similarly as if you would do a regular infinite, however the character drops with every volley and eventually the combo must be broken therefore removing the infinite concept similar to a wall. The only time you can perform 100% with it is when damage protection is not enabled but the attack patterns technically do in fact have to be changed towards the end.
