rarepairs or, like... medium-rare pair?

i subscribe to the rec center, which is a weekly email that gathers up articles on recent fandom goings-on, older things that might have been missed or are just cool, some fanart, and (of course) a handful of recs from a huge spread of fandoms; occasionally the rec lists are themed, and/or they do a fandom or ship explainer with recs to go with it (i did an overwatch explainer for them... wow, that was over 2 years ago now).

anyways, they put out a call for rarepair recs and of course, now i'm thinking about what exactly constitutes a rarepair.

( personally i'm a medium/medium well person, but, eh. )