OR

• a logical binary relation that is true if any argument is true, and false otherwise;

• [o]estrogen receptor;

• odds ratio;

• oil retention [enema];

• oligomer of resveratrol;

• open reduction;

• open repair;

• operating room;

• optic radiation;

• oral rehydration;

• orbicularis oris [muscle];

• orosomucoid;

• orthopedic;

• orthopedic research;

• ouabainresistant;

• outwardly rectifying [current];

• oxidized radical

• rate of outflow