Definitions of preventive detention
the imprisonment of a person to stop them from committing further offences or in an effort to maintain public order
A repeat offender who molested two young girls on their way to school was sentenced to seven years' preventive detention.
the imprisonment of someone who has not necessarily committed a crime, but who an authority thinks is a danger
"I don't agree with preventive detention as being in principle a tool, even in wartime," he said.