New Old Stock
The term New Old Stock (NOS) means “new from old stock”. It refers to components and devices whose production has been discontinued but which are available, for example, from spare parts stocks (unused).
The term is also used for components or equipment that were manufactured before new regulations were issued and therefore may not comply with them, but may still be sold (for a transitional period) or used (including for replacement needs). An example of such a regulation is the EU RoHS Directive, which bans the use of some harmful substances such as lead, mercury and cadmium in electrical and electronic equipment since 1 July 2006. This is intended to ensure that, as far as technically possible, the hazardous substances do not enter the environment either during production or during subsequent disposal.
Another example are electron tubes, which today have been largely replaced by semiconductors, but are still very popular in some applications, e.g. for high-end hi-fi or guitar amplifiers. Tubes from manufacturers that no longer exist are sometimes still available from old military spare parts stocks. They partly have different characteristics than tubes from current production and are therefore sought after.
Confusion of the term
Easily confused with the identical abbreviation NOS(Never Outof Stock), which stands for permanent availability. Due to the similarity of the abbreviations, misunderstandings are possible, especially with regard to product designations in online shops.