According to the Queen's Regulations and Orders:
"(1) The Chief of the Defence Staff or such officer as he may designate may appoint a corporal as a master corporal.
(2) The rank of a master corporal remains that of corporal.
(3) Master corporals have seniority among themselves in their order of seniority as corporals.
(4) Master corporals have authority and powers of command over all other corporals." — QR&O 3.08
Master Corporal, while formally an appointment, is treated as a de facto non-commissioned member rank, and is often described as such, even in official documents.
As mentioned above, the Master Corporal is senior to the Corporal (and its Naval counterpart, Leading Seaman). It is junior to the rank of Sergeant (Sgt) and its equivalent naval rank, Petty Officer 2nd Class (PO2). Master Corporals and Master Seamen together with Corporals and Leading Seamen make up the cadre of junior non-commissioned officers.
The rank insignia of a Master Corporal is a 2-bar chevron, worn point down, surmounted by a maple leaf. Embroidered rank badges are worn in "CF gold" thread on rifle green (Army) or Air Force blue (Air Force) melton, stitched to the upper sleeves of the Service Dress jacket; as miniature gold metal and rifle-green enamel badges on the collars of the Army dress shirt and Army outerwear jackets; in "old-gold" thread on Air Force blue slip-ons on Air Force shirts, sweaters, and coats; and in tan (Army) or dark blue (Air Force) thread on CADPAT slip-ons on the Operational Dress uniform. Insignia for mess kit is determined by branch or regimental tradition.
Master Corporals are generally initially addressed as "Master Corporal Bloggins" and thereafter as "Master Corporal". The slang term "Master Jack" is never used as a form of address.
However, certain trades have their own particular qualifications in addition to the above. For example, infantry combines the Qualification Level 5B course, Qualification Level 6A, and Junior Leader's course in a single Infantry Section Commander's Course. In addition to be promoted to Master Corporal an infantry soldier must have a machine gunner's specialization course.
Master Corporals often serve as Training Non-Commissioned Officers for the purposes of training new soldiers. They are often a new recruit's first taste of military life.