ANSWER:

A lockdown is a requirement for people to stay where they are, usually due to specific risks to themselves or to others if they can move freely. The term "stay-at-home" or "shelter-in-place" is often used for lockdowns that affect an AREA, rather than specific locations.

The term is used for a prison protocol that usually prevents people, information or OBJECTS from leaving an area. The protocol can usually only be initiated by someone in a position of authority.

A lockdown can also be used to protect people inside a facility or, for example, a computing SYSTEM, from a threat or other external event. In buildings doors leading outside are usually locked so that no person may enter or exit. A FULL lockdown usually means that people must stay where they are and may not enter or exit a building or rooms within it, needing to go to the nearest place designated safe if not already in such a place. A drill lockdown may be held in the absence of a threat, to familiarise people with what they must do