A person, place or thing that is actively supportive of homosexuals and homosexuality.
SUSIE: Hey Billy, what did you do this weekend?
BILLY: Not much. Went to Church with my Mom.
SUSIE: Church? But you're a homo.
BILLY: True, but this particular congregation welcomes homosexuals and believes that Jesus wouldn't judge us as wicked.
SUSIE: Oh, so your Church is pro-mo?
BILLY: Yes, it is pro-mo.