A bro is almost always a white teenage boy. The title 'bro' probably emerges from the 'brotherly' nature of such people. They are usually impossibly close friends with a small group of males, said to be as close as 'brothers.' Hence the term 'bro.' They typically lose the title of 'bro' when going on to college or other auspices of 'pwnage' or '0wnage.' However, this is a sad irony considering many bros have been born and raised in the same environment their whole life and as such are well-taken care of ninnies who work out alot and obsess about their appearance. Therefore, they do not often advance to a genuine 'college' setting.
A bro is typically seen sporting all the latest and most expensive brands of clothing. A bro will make his parents go to the furthest extent of financial deploritude to pay for such clothing. Bros almost inevitably end up dating bitches, who are usually pretty hot. But, more or less on the mental level of an insect. However, their extreme 'hotness' redeems them from any serious character scrutiny, and actually boosts the social position of the bro they have chosen to date.
Overall, a bro will conform to the extremest extent of fashion, behavior, humor, and religious beliefs or moral values of their immediate community, mostly from fear or failure to critically think.
A good example of a bro would be Spencer Pratt; he is exceptionally good-looking, also exceptionally retarded and has a skill for getting his ass kicked by Al Roker. Also, he is a good example because his girlfriend is hot, and very, very stupid. Together they are known as Speidi. (Heidi+Spencer)