lockdownlock·down /ˈlɒkdaʊn $ ˈlɑːk-/ noun [countable, uncountable] 
1a time when prisoners are not allowed out of their rooms, usually after there has been violence in the prison2a time when all the doors in a building are locked in order to protect the people inside from danger: 
The school went into lockdown after the shooting.
1a time when prisoners are not allowed out of their rooms, usually after there has been violence in the prison2a time when all the doors in a building are locked in order to protect the people inside from danger: The school went into lockdown after the shooting.