COMPREHENSIVE MAJOR MEDICAL: A type of medical insurance developed to meet the need for protection against a broad range of catastrophic medical expenses, whether incurred in or out of the hospital. The major medical expense benefit usually is subject to a deductible.
HOWEVER, that being said, each insurance carrier has a different explanation for what exactly is covered under Major medical. (Full disclosure: I am a benefits consultant and work with various insurance carriers.) As I mentioned, each carrier's definition is different. So the best place to find out exactly what is covered under your plan is to go to your benefits booklet or contract.
Hope this helps.