Naturism is a lifestyle of practising non-sexual social nudity in private and in public; the word also refers to the cultural movement which advocates and defends that lifestyle. Both may alternatively be called nudism. Though the two terms are broadly interchangeable, nudism emphasizes the practice of nudity, whereas naturism highlights an attitude favoring harmony with nature and respect for the environment, into which that practice is integrated. That said, naturists come from a range of philosophical and cultural backgrounds; there is no single naturist ideology.
Ethical or philosophical nudism has a long history, with many advocates of the benefits of enjoying nature without clothing. At the turn of the 20th century, organizations emerged to promote social nudity and to establish private campgrounds and resorts for that purpose. Since the 1960s, with the acceptance of public places for clothing-optional recreation, individuals who do not identify themselves as naturists or nudists have been able to casually participate in nude activities. Nude recreation opportunities vary widely around the world, from isolated places known mainly to locals through officially designated nude beaches and parks and on to public spaces and buildings in some jurisdictions. (wkipedia)
Charles writes about outdoor activities, he also practices naturism.