Definition 1: Kokichi x Himiko.

Definition 2: The greatest and purest pairing of all time. It’s god-tier. It’ll cure your depression and make your life always sunny and full of rainbows. Well, unless you have shit taste, then it’ll end up poisoning you; but if you don’t like oumeno then that’s only for the greater good.

It’s an acronym standing for Can’t Remember A Fucking Thing. It’s usually used to describe embarrassment at being unable to remember someone (CRAFT moment); going onstage as the lead in the latest theatrical performance and your mind goes completely blank (CRAFT situation); the next morning after a night when you got pissed as a fart and woke up in bed cuddling a traffic cone and a string of fairy lights wound round your prick.

Oumeno is a ship from Danganronpa V3, which contains Kokichi Ouma and Himiko Yumeno.
It's a ship that while loved, is completely toxic and a common trigger in the fandom.
Kokichi constantly bullied Himiko and also accused her in chapters 2 and 3 despite him knowing she couldn't have done it.