If there is a lockdown in a building or the building is on lockdown, nobody is allowed to enter or leave because of a dangerous situation.
The lockdown lasted for about an hour until the intruder was arrested.
The prison was put on lockdown after riots broke out.
lockdown in British English
(ˈlɒkˌdəʊn)
noun
US
a security measure in which those inside a building such as a prison, school, or hospital are required to remain confined in it for a time
many schools remained under lockdown yesterday
lockdown in American English
(ˈlɑkˌdaʊn)
noun
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
Examples of 'lockdown' in a sentence
lockdown
London was in a virtual lockdown after two days of drama and terror.
Times, Sunday Times (2013)
An international financial centre was put on lockdown for a day.
Times, Sunday Times (2014)
Heathrow on a security lockdown yesterday.
The Sun (2016)
Iraq was in lockdown yesterday as voters cast their ballots in the first national elections since the withdrawal of US troops two and a half years ago.
Times, Sunday Times (2014)
ARMY bases were in lockdown yesterday and thousands of soldiers put on'high alert' after a second security scare.