When a girl that has a boyfriend or has no romantic interest in you says you are cute or adorable like a kitten or a similar cute, small, and furry animal.
It's similar to being put in the friendzone but better.
Girl with platonic feelings: Aw, you're so adorable.
Boy with a secret awkward crush: How so?
Girl with platonic feelings: Like a kitten or lemur!
Boy with a secret awkward crush: Uh...hah...? Thanks...
Interlocuter: Oh no! You've been kittenzoned!
Boy with a secret awkward crush: At least we're friends and I'm cute?