an emergency security practice in which prison inmates are locked in their cells and denied the usual privileges of dining, showering, etc. outside of them
See lockdown in American Heritage Dictionary 4
noun
The confinement of prison inmates to their cells as a security measure following a disturbance in the prison.
A prison, especially a high-security one.
A device that secures a piece of equipment, especially a computer, so that it cannot be moved or stolen.