Non-commissioned officers are personnel in the military who have attained their rank through merit rather than in a commissioned officer's position, which they hold through education or commission. To avoid repetition, synonyms for the term "non-commissioned officer" include "enlisted personnel," "sergeants" or "NCOs." Some military organizations may also refer to them as "specialists" or "corporals," while others may use terms such as "petty officer," "staff sergeant," or "master sergeant." These synonyms are used to denote a level of rank and expertise in a specific field, indicating that these personnel have achieved a certain level of skill and experience.