A professional affiliation is an organization or group a person belongs to based on involvement in a particular profession. A nurse could become a member of the American Nurses Association, for instance. Affiliations range from paid membership to active involvement in organization activities or leadership roles.
People often include a section on their resumes labeled "Professional Affiliations." Revealing participation in professional groups may convince a hiring manager that a person has genuine passion for a career. It also suggests a desire to get involved beyond common work requirements. A person may also hold an officer position in the affiliated organization.