Is there anything specific you are looking for clarification on?
NARSUM=Narrative Summary (the docs write-up on what makes you unfit and why medically)
MEB=Medical Eval Board
PEB or IPEB=Informal Physical Eval Board (who says if you are fit or unfit for service)
PEBLO= your liaison in the whole process
MSC=Military Service Coordinator (the person from the VA that helps you)
FPEB=Formal Eval Board (after the IPEB, if you appeal the results...to overturn being unfit or to add conditions)
VARR=VA Rating Reconsider (to "challenge" the ratings the VA recommends for the unfit conditions only)
Providence= The location of the VA office that handles the unfit cases for Air Force
OAC=Office of Airmen's Counsel (your medical board lawyer if you need one)
Impartial Review=unbiased 3rd party to review your case before going to IPEB
That's all I can think of right now.