| MAR | main admissions room; marasmus; marrow; maximal aggregation ratio; medication administration record;... |
|---|---|
| MER | mean ejection rate; medical emergency room; methanol extraction residue; murmur/energy ratio |
| OOR | out-of-room |
| OR | a logical binary relation that is true if any argument is true, and false otherwise; [o]estrogen rec... |
| ORN | operating room nurse; orthopedic nurse |