I first heard the term shortly before I separated from the military, in the context, "Don't become a dependapotamus." I wasn't sure whether to be amused or offended, but quickly decided on amused.
There are a few definitions out there, but Urban Dictionary has the simplest one:
If you prefer a visual representation, look here.
Commonly used military terms and acronyms:
BX (n.) Acronym for Base Exchange. A store on base selling a variety of goods, comparable to Target or Walmart, but purchases are tax exempt. Alternately know as PX (Post Exchange).
Class Six (n.) The tax exempt liquor store on a military base.
Commissary (n.) The tax exempt grocery store on a military base.
PCS (n.) Permanent Change of Station. A military move.
FRG (n.) Family Readiness Group. A group created to enhance information sharing between Army soldiers and families. Especially active during deployments.
I will add to this list as I continue blogging. Please let me know if there are any additional terms that I need to define.