O:
Objective (as in SOAP note)
O2
Oxygen
OB
Obstetrics
OBGYN
Obstetrics-gynecology
od
Once daily
ODM
Opponens digiti minimi
OKC
Open kinetic chain (CKC =?)
OOB
Out of bed
O.P.
Outpatient
OP
Opponens pollicis
O.R.
Operating room
ORIF
Open reduction internal fixation
OSW
Oswestry disability index
OT
Occupational therapy or occupational therapist
OTC
Over the counter
OTR
Occupational therapist (what they follow their signatures with)
oz.
Ounce