In the U.S. Army & Marine Corps, an enlisted job is called an "MOS" (Military Occupation Specialty). In the U.S. Navy & Coast Guard, an enlisted job is called a "Rating". In the U.S. Air Force, an enlisted job is known as an "AFSC" (Air Force Specialty Code).

The 4th digit in the AFSC indicates an individual's skill-level. For example, someone with the AFSC "1A251" has a "5" skill-level. An individual receives the "1" skill-level when they enter technical school for the AFSC. Upon graduation from technical school, they receive the "3" skill-level. Individuals are normally awarded the "5" skill-level after a period of on-the-job training (OJT) and correspondence courses, or "CDCs". Depending on the job, this process can last anywhere between 12 and 18 months. Upon promotion to Staff Sergeant (E-5), individuals enter training for the "7" skill-level. This level of training consists of more CDCs, OJT and, for some jobs, a seven-level technical school.