lock·down 
(lŏkdoun′)
(lŏkdoun′)n.
1.
a. A protocol followed in an emergency that involves confining people in a secure place, such as the confinement of prison inmates in cells after a disturbance, or the locking of students and teachers in classrooms after a violent attack.
b. A situation in which this protocol is undertaken.
2. A facility, such as a prison, where people considered to be dangerous are locked inside living quarters or otherwise confined.