Abbreviation of Poor Oral Hygiene.
Probably quite popular term among the dentistry profession.
If someone isn't in a routine of brushing their teeth often and just generally keeping their breath smelling minty and inoffensive you might feel inclined to say:
"wow, that rancid old man is breathing on the other side of the bus and I can smell the stench of Worthers Original and pipe smoke on his breath. He must have very pooral hygiene"