A parking space in a "Multilevel Parking Facility" (Parking Garage) which is actually not a legitimate parking spot, but would make sense if it was. In fact, not spots are often mistaken for real parking spots, and used without consequence.
John: The garage was full today, so I parked in this not spot.
Bill: Wow...I've never even realized that wasn't an actual spot.
John: Heh, neither have the rent-a-cops; I've never seen anyone get a ticket for parking in that one.
Somewhere you can't get a mobile phone/cellphone signal or car radio signal
Say that again dude - you must of hit a not spot