A young person who has grown up in a military family, especially one that often moves to new assignments.
An army brat can end up attending numerous different schools in different parts of the country -- or around the world -- over the course of only a few months. Army brats often complain about being unable to make friends because they don't live anywhere long enough to really get to know anyone.
When they grow up, former army brats often end up being more independent and resourceful because of their mobile childhood, but they sometimes feel isolated and rootless because they missed out on many things -- homecoming games, prom, yearbooks, sports, lots of friends -- that other kids took for granted.