What term describes the capability or proficiency to perform a function?

The term that best describes the capability or proficiency to perform a function is "competency." Competency refers specifically to the ability to carry out a role or task effectively, which encompasses a person's skills, knowledge, and behavior in a given field. It indicates not just the presence of relevant skills but also their application in real-world scenarios, making it a comprehensive term for assessing an individual’s effectiveness in performing specific functions.

Other terms have more specific or slightly different meanings. "Skillset" generally refers to a collection of skills that an individual possesses, without necessarily assessing their proficiency. "Competence" is often used interchangeably with competency, but it is usually more about meeting minimum standards rather than demonstrating exceptional capability. "Expertise" implies a higher level of knowledge and mastery in a particular area, indicating someone who is highly skilled, but it does not encompass the broader range of ability that competency does. Thus, "competency" is the most accurate term for describing the general capability to perform a function.