Aptly stands for 'Super Tan Girl'; a combination of a Gina and
Valley Girl into one entity. Usually
blonde, but is based on the overexcessive and obvious fake bake the girl has undergone.
Also associated with the more
popular crowd, but not necessarily meaning that they are.
"Do you
think that she went on vacation?"
"No, she's just an STG"
or
"
That girl over there is such an STG"
"tell me about it, she could support the whole bronzing industry
single-handedly"