I've seen this jargon around and use it myself but now that you ask I'm not sure where I first saw it.

tl;dr - good faith requires you to understand and do your best to represent the other side, not cherry pick sneaky "wins"

When I use the term my intent is to frame the opposing argument as strongly and clearly (and fairly!) as possible so that you can make your own point strongly and fairly. The critique of a "strawman argument" is a metaphor about arguing/fighting a training dummy instead of an actual enemy, usually by addressing only part of an argument or by ignoring context or using logical fallacies like motte and baily or false dichotomies. The idea is that it's very easy to look like your point wins when you fight the scarecrow; if it's actually a good argument face it off against the knight in armor actually fighting back.