zero clearance

"Zero clearance"

I hear people talk about this now that it's getting colder outside.
Is this a phrase or an item. Someone I asked said it had something to do with safety.

I've never heard of zero clearance. You don't mean zero tolerance, by any chance? In case you do, zero tolerance is a phrase coined (I think) by New York's last mayor, Mayor Giuliani, to describe a policing policy where any crime or misdemeanour would be cracked down upon and prosecuted, however minor it may have been. Nothing would be ignored or tolerated - hence zero tolerance.