1. Licensed physician or any qualified health care practitioner who provides health care services to the patient and is legally accountable for establishing patient diagnoses. If a medical doctor, the provider can be the attending, ordering, treating, performing, or referring physician. 2. Organization, institution, or individual that provides health care services to Medicare beneficiaries. Physicians, dentists, pharmacists, ambulatory surgical centers, home health care agencies, skilled nursing facilities, and outpatient clinics are some of the service providers covered under Medicare Part B. 3. In a 401(k) defined-contribution pension plan, a financial services company that offers the mutual funds and other investment choices.