A strip search is a practice of searching a person for weapons or other contraband suspected of being hidden on their body or inside their clothing, and not found by performing a frisk search, by requiring the person to remove some or all of his or her clothing. The search may involve an official performing an intimate person search and inspecting their personal effects and body cavities (mouth, vagina, anus etc.). A strip search is more intrusive than a frisk and requires legal authority. Regulations covering strip searches vary considerably, and may be mandatory in some situations or discretionary in others.
A strip search in BDSM context should of course always be consensual, or at least be discussed before it happens, even if afterwards applied as a surprise. It can obviously be a game offering mutual fun, if performed within a role play scene of being a prison guard or being arrested by the police.