What is Mine and Theirs when merging branches?

Quite the beginner question, but I would like some confirmation regarding solving conflicts when merging branches. I find terms and error messages often quite ambiguous. I’m currently in the proces of bringing a year old, discontinued feature-branche from the grave, by merging it into a separate just-made up-to-date branche. In doing so, 250+ conflicts rose. Since you often can’t undo a ‘Resolve using mine/theirs’, I just want to make sure I don’t screw up halfway :) So, I’m in this new branche, where I merged a different, older (not relevant, I assume?) branche. To which branche refers mine and theirs? You’d assume that ‘theirs’ refers to the other branche you are merging, but I’ve multiple times selected ‘mine’ and saw a local edit been removed. Hence the ambiguity
1 answers

Mine is the version that was opened in your modeler before doing any merging. Theirs is the branch you are merging from.

What do you mean by a local edit has been removed? Is it no longer showing this microflow as changed? Did actions in it change? Was it saved before merging?