What is... a rarepair?
Rarepair refers to a rare pairing inside a fandom. This means that a pairing that someone ships does not have a lot of fanart or fanfiction about them or anything at all.
While crackships are always rarepairs, these rare pairings can make a lot of sense in canon, but they are just not that popular. But they often also refer to shipping characters that do not interact in canon at all, maybe not even know each other in the source material.
There are no exact numbers on when a pairing is considered a rarepair but some characteristics are that the tag on AO3 does not have a lot of hits and that most of the entries were written by the same person.
Shipping a rarepair can be frustrating, when you feel like you are alone in your love for a pairing, but it can also be fun to be able to shape the pairing together with two, three other shippers however you want them, because you basically own the ship by solely contributing to it.
Once again here to bring you stupid memes to illustrate my point.
Tell me about your rarepair. You're also welcome to illustrate your point.