A mobro could refer to a Mormon Brony, since it is a combination of "Mormon" and "brony". This is unofficial, and my only source is that I am Mormon and have heard mormons use this term, even I've started using it to describe myself, since I am also a brony. If you don't know what a brony is, it's a person outside of the target audience group who watches My Little Pony: Friendship is Magic. Brony is the combination of the words Brother and Pony.