In the middle of a “combo”, if specific attacks (among other things) hit, then the damage correction from the combo so far will be reset; then the damage of the moves will be back to their original values. This is one of the meanings that the term “reset” has in relation to combos (the correction resets).
The other meaning of “reset” involves cutting off the combo itself temporarily (so that it is not a true combo, but usually very very close; the combo resets). So, in the middle (or at the end) of a combo, intentionally interrupting its flow by mixing in, say, an overhead move or something with a slow startup (which will also stop the hit count as well as reset the correction), then starting the combo once more, the total damage will be increased so long as this window of opportunity isn’t used to escape.
The former is mostly found in 3D fighting games. The latter is often found in 2D fighting games when it comes to things like custom combos, but in combo games, where even normal combos can get long-winded, resets of both stripes are also used.
The term “reset” has usually been used for the latter definition in the past, but recently, the former definition has made its way into more games.