OD's 'n' things
RETDPI
It also used to stand for " Other Denominations " when we used to be divided up into C of E's, R.C.'s and O.D.'s.
When we had Drumhead church services the order " Fall out the Roman Catholics and Jews " was given and they/we marched to the edge of the parade ground and stood at ease with backs to the service.
One non-participant in the service was heard to say " Jaysus, Seamus, I never realised that you were Jewish."
I imagine things have changed.