A term that is massively overused. It usually means a man/woman who only judges by looks and not by personality.
Many ugly girls consider guys shallow just because they get turned down by them and vice versa. A lot of ugly guys think girls are shallow because they get turned down. But neither of these are true.
The true example of shallow is when a guy/girl base someone's personality on how they look. If you're confused read below.
I was hanging out with my friend the other day who is quite a bit better looking than me (I'm not ugly, he's just hot I guess). So he and I are hanging out with this girl from school and I decide to test something.
Early that day I tell her a joke and she kind of laughs. So about 6 hours later, I have my friend tell her the exact same joke, word for word and she cracks up like it's the funniest thing she's ever heard.
Apparently the same exact joke was funnier when told by him, just because he's better looking. Avoid girls/guys like that at all cost.