A term coined by the members of Glo Gang/Glory Boys Entertainment (GBE). The act of bettering yourself as a person, whether it may be by getting your money up or changing your ways. It was high jacked by wypepo (as most things of black culture are) and twisted to mean when someone goes from ugly to pretty over a period of time.
A twist of the phrase "grow up", referring to a person's incredibletransformation. This is usually based on increase of style and self-confidence (and potentially one's squad).
Noamee: "Remember that kid nerdy kid Loganus from High School?"
Mayana: "Yeah but have you seen him now?!?! GLO-UP!!!!"
Noamee: "I wish a nigga would"
A glo up is when someone becomes confident, and believes in themselves, and they don't give a fuck about what anyone says about them. That's what makes them seem more beautiful.
S/he had a glo up because they believe in themselves and has become more attractive.