Definitions by JhB
Army Brat
Any child who has grown up with a parent in the army, has never lived in a place more than 3 years, knows what tdy means, got excited when you turned 10 because you get a military id, shops at the px/bx, personally know 10 or more people who got sent to Iraq, lived overseas (hawaii counts) and while overseas attended an international school, has always lived in a place that started with "fort" or ended in "AFB".
TDY
when a person in the military is temporarily deployed for a year, aka being sent overseas, generally without the rest of the family.