Fatigue is one of the most common symptoms experienced by older people, both with and without chronic disease. It is unpleasant and distressing and can affect functioning and quality of life. Fatigue also may inhibit an older person from participating optimally in a physical therapy program aimed at rehabilitation or the promotion of better health. However, confusion surrounds the concept of self-reported aging-related fatigue, not only because of the complexity of the problem itself but also because of lack of clarity of definition and the use of the term "fatigue" to describe a range of different concepts. This article aims to provide clarification of the concept in the context of physical therapist clinical practice. The intention is to increase awareness of the issue among physical therapists, promoting their assessment and consideration of the problem when planning health interventions involving functioning, physical activity, and exercise for older people.