When a school or other place is locked down, it means that the doors are closed and no one is allowed in or out. This is usually done to protect the people inside from danger.
The school was placed on lockdown after a shooting was reported.
The airport was placed on lockdown after a bomb was discovered.
noun
the act of confining prisoners to their cells (usually to regain control during a riot)
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I guess it will not be for lockdown.
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That is why the article is on lockdown.
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Lots of schools are on lockdown.
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The article was then under lockdown.
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As a precaution, the school was put into lockdown.
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But again, I insist on a lockdown.
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This was the first lockdown in the history of the plant.
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The school was put on lockdown for the rest of the day.
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GAB will probably do the same as well as Lockdown.
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A sudden and unexplained facility lockdown extends into a long term quarantine.