A girl who a guy marries if they're in the military and don't want to live in the barracks. In the military, one gets paid an allowance for being married, so they often have fake marriages, or marry people they barely know.
Most BAH wives are
1)illegal immigrants who get green cards out of it
Wow, Tegan got married after knowing that guy for three weeks?!
Well, she's only a BAH wife, she's ugly and now they don't have to live in the barracks anymore.