The terms exercise and physical activity have very similar meanings. However, experts now agree that physical activity is a term that has a much broader meaning than the word exercise. Physical activity includes many types of activity, such as exercise, sports, dance, recreational activities, and lifestyle activities. Exercise is one type of physical activity that is primarily used to build physical fitness. For example, muscle fitness exercises are referred to as exercises because they are designed especially for building muscle fitness. These and other exercises (such as flexibility exercises) are types of physical activity but are also considered exercise. Sports and dance are also types of physical activity but are not generally classified as exercise. Sports and dance could be done for fitness but are also frequently done for other reasons, such as having fun and being with friends. Some people do not understand the difference in terms, so it is not unusual to see the terms used interchangeably.