What is this rule for all inís?

So I posted on Reddit asking about how if I understand side pots completely and showed them a poker journal Iím making with the side pot part. I then got a comment saying I left out this:

since youíre looking for completeness, what you missed is that certain all in bets re-open action and certain all-in bets donít.

ďIf I bet 30, player 1 calls, and you go all in for 31, I canít reraise nor can player 1. different rules prevail in different situations and cars rooms. sometimes if the raise is 50% of the original bet thatís enough to reopen and more commonly a minraise is the amount to reopen. these rules describe the situation necessary to create a sidepot when the allin is greater than the original bet but not enough to reopen bettingď

What exactly is this term called and can someone explain it better or at least link a video or article that does?