Longman Dictionary of Contemporary English
Wikipedia
Preventive detention is an imprisonment that is putatively justified for non- punitive purposes.
A related, but different form of detention, is detention of suspects or remand. In contrast to preventive detention, detention of suspects must quickly be followed by a criminal charge (or happen after the charge).
In most jurisdictions, people suffering from serious mental illness may be subject to involuntary commitment under mental health legislation. This is undertaken on health grounds or in order to protect the person or others. It does not strictly speaking constitute a form of preventive detention, because the person is detained for treatment and released once this has proven effective.
Usage examples of "preventive detention".
He was searching for some reason to slap me down, either with his fists or with a preventive detention arrest.
We think Bury was behind this rebellion, but there's not enough evidence to put him in preventive detention.
Without Harry Kelly, I would most likely have been in prison at that moment-or in a preventive detention apartment with federal plain-clothes guards standing watch at the doors and windows.