This code system http://hl7.org/fhir/us/pacio-fs/CodeSystem/pacio-cat-fs defines the following code:

Code	Display	Definition
functioning	Functioning	Functioning is an umbrella term for body function, body structures, activities, and participation in societal roles. An individual’s functioning represents a dynamic interaction between their health condition, environmental factors, and personal factors. Taking a broad view of health that encompasses physical, mental, and social well-being, includes optimizing functioning as a component of optimizing their health. Characterizing an individual’s functioning includes both understanding the severity of an individual’s signs, symptoms, impairments and limitations, and how they correspond with day-to-day activities. Functioning also serves as a key health outcome within health care.