NOTAM is an abbreviation for Notice To AirMen. The Aeronautical Information Manual in Chapter 5-1-3 defines it as
Time-critical aeronautical information which is of either a temporary nature or not sufficiently known advance to permit publication on aeronautical charts or in other operational publications receives immediate dissemination via the National NOTAM System.
It goes on to say that it is information that could affect your decision to fly
When I say I did a flight with no GPS is a NOTAM , I am being sarcastic but the truth is basically every plane has a GPS and it was noteworthy to me. I was taking my family to Columbia O22 in the foothills of the beautiful Sierra Nevada Mountains on Mother's day. I have been there before and knew the way so I shouldn't be worried, right? I saw a VOR in the plane so no biggie I will just plan the flight use the VOR as back up. Well..........I was borrowing the plane and didn't know the VOR was working, till I tried to use it. I actually (more sarcasm) found my way the old old fashion way Pilotage and Dead Reckoning (comes from deduced reasoning in otherwords if I know I am traveling at X speed, and the distance to travel is X I will be at point B at X time) .
I learned as a pilot that day that the emphasis I put on Pilotage and Dead Reckoning really is useful and to be honest kinda fun flying like that. Don't get me wrong I love GPS, it does free you to focus on all the other things there are but when the GPS is backed up with strong map reading skills and deduced reasoning (and a VOR when it works), you will not run into problems finding your destination.
P.S.flying to the Columbia airport is a great trip, the town is preserved as it might have looked in old mining days