New Old Stock refers to parts which may have been manufactured long ago but have never been used. These parts may not be produced anymore, and the new old stock may represent the only way to get a particular part.
Most NOS parts have been on shelves, moved from place to place, taken out of their packets or kept in storage. Over time they may have developed some damage and discolouration to the original packaging or the original packaging may be missing. This minor damage from shelf life does not detract from an item being identified as NOS.
New Old Stock is also referred to as NOS, New Obsolete Stock or New Original Stock.