M&F (mother and father)

M1 (mitral first sound)

M2 (mitral second sound)

MA (medical assistance; mental age)

mAb (monoclonal antibody)

MABP (mean arterial blood pressure)

MAC (mycobacterium avium complex)

MAC (monitored anesthesia care)

MAD (multiple autoimmune disorder)

MADD (mothers against drunk driving)