While we are at it. NOS
New
Old
Stock
ie, something was "new" (when it was made) but is now old, but that hasn't been used. So lets says you come across a Scarf mount for a Brisfit BE2 WW1 fighter, never issued, no wear. So it is new in the sense that it hasn't been used. But if made in 1915 then you can't really say it is new. Hence why "NOS" rather than "New".
Don't laugh at the scenario. I recall the story that in either the 1970s or 1980s the Shuttleworth trust were having a torrid (pun) time trying to recreate the nose cowl for either a Sopwith Scout or Camel. Apparently it was on those lost art techniques to do so. An appeal for help to the RAF resulted in the supply of an NOS
item. Shuttleworth had been thinking more along the lines of a project to torment the aero apprentices.
You just never know what is lurking in dark corners.......