As far as I know, it's a term used mainly by American auctions to describe a car. The term sits between 'original' and 'modified'. Whereas the term 'original' implies that a car hasn't been restored, 'survivor' implies that it is 'largely' unrestored but will have had some work carried out to keep it on the road. A 'survivor' is also the sort of car that can be used - as opposed to an 'original' low mileage example which will probably cover very few miles. In some circles it can get quite specific - certain American car clubs, for example, have a 'survivor' category which stipulates a model must be over 20 years old and 50% unrestored as well as driving to the show.