BDSM actions can often take place during a specific period of time agreed to by both parties, referred to as "play", a "scene", or a "session". Participants usually derive pleasure from this, even though many of the practices — such as inflicting pain or humiliation or being restrained — would be unpleasant under other circumstances. Explicit sexual activity, such as sexual penetration, may occur within a session, but is not essential. Such explicit sexual interaction is, for legal reasons, seen only rarely in public play spaces, and it is sometimes specifically banned by the rules of a party or playspace. Whether it is a public "playspace" — ranging from a party at an established community dungeon to a hosted play "zone" at a nightclub or social event — the parameters of allowance can vary. Some have a policy of panties/nipple sticker for women (underwear for men) and some allow full nudity with explicit sexual acts.