Naturism is the philosophy and practice of being naked. It applies to being naked indoor (in own house, sauna, swimming pool, parties etc.) or outdoor (swimming, sunbathing, walking, sports etc.).
Similar terms are nudism (although there are controversies about it, because in some countries term naturism means being naked without any sexual context, while nudism is not considered so restrictive in that area). In German-speaking area it is commonly known as FKK (Freikörperkultur).