Sergeants major is a senior non-commissioned

Non-commissioned officer

A non-commissioned officer , called a sub-officer in some countries, is a military officer who has not been given a commission...

 rank

Military rank

Military rank is a system of hierarchical relationships in armed forces or civil institutions organized along military lines. Usually, uniforms denote the bearer's rank by particular insignia affixed to the uniforms...

 or appointment in many militaries around the world. In Commonwealth

Commonwealth of Nations

The Commonwealth of Nations, normally referred to as the Commonwealth and formerly known as the British Commonwealth, is an intergovernmental organisation of fifty-four independent member states...

 countries, Sergeants Major are usually appointments held by senior non-commissioned officer

Non-commissioned officer

A non-commissioned officer , called a sub-officer in some countries, is a military officer who has not been given a commission...

s or warrant officer

Warrant Officer

A warrant officer is an officer in a military organization who is designated an officer by a warrant, as distinguished from a commissioned officer who is designated an officer by a commission, or from non-commissioned officer who is designated an officer by virtue of seniority.The rank was first...

s. In the United States, there are various degrees of sergeant major (Command Sergeant Major (CSM), Sergeant Major of the Army (SMA)

Sergeant Major of the Army

The Sergeant Major of the Army is a unique non-commissioned rank in the United States Army. The holder of this rank is the most senior enlisted member of the Army, unless an Army NCO is serving as the Senior Enlisted Advisor to the Chairman, when in that case that NCO will be the most senior...

, Sergeant Major of Marine Corps), but they are all of the same pay grade

Pay grade

Pay grades are used by the uniformed services of the United States to determine wages and benefits based on the corresponding military rank of a member of the services...

.
In most Commonwealth forces, Sergeant Major is a rank, but rather an appointment held by a warrant officer

Warrant Officer

A warrant officer is an officer in a military organization who is designated an officer by a warrant, as distinguished from a commissioned officer who is designated an officer by a commission, or from non-commissioned officer who is designated an officer by virtue of seniority.The rank was first...

.