Landing Zone. Originally came into use during the Vietnam War to address the area where a helicopter would be a landing. A "hot LZ" is a zone in which charlie still had a significant presence, and thus was dangerous to land in.
Since Vietnam, the term has come into the modern vernacular to mean any bad, rough, or uncomfortable situation.
1. Request to land denied, that LZ is hot, repeat, that sector is Victor Charlie.
2. I was riding dirty the other night when I drove right into a police sobriety checkpoint. Talk about a hot LZ.