Has your home or workplace (or a place you've been that's not either) ever been put into 'lockdown'?

I've never experienced anything like it so really have no idea what a 'lockdown' is apart from the ones that government's and law enforcement as agents of government tried to enforce during Covid years. They aren't really what most people would think of when 'lockdown' gets mentioned.

What a 'lockdown' at someone's place of living, or someone's workplace, would be like is unclear. I'm sure government installations all have very specific security plans which includes implementing lockdowns.

So - ever been in one? Ever had to implement one?