So, imagine you have a group of friends or people that you hang out with a lot. The way you act or talk around them might be different from the way you act or talk around your family or other people.
Well, some people have a group of friends that they call their "bros." These friends like to do certain things together and they have a certain way of talking to each other. This group of friends is called the "bro subculture."
They might use certain slang words or phrases that are unique to their group. They might wear certain clothes or listen to certain types of music that they all like.
Overall, it's just a way for these friends to feel like they belong to a special group and have things in common with each other. It's kind of like being part of a club or a team.