A person who tries to be like
everyone else and epically fails. Someone who thinks
that looking like
a barbie doll is "cool" or caking
makeup on their faces makes
them look any better. A person who pretends to be someone they're not.
For example, Miley Cyrus is a poser because
to be someone who doesn't even exist and then goes around kissing every co-star she gets
(which makes her a slut).