What it should mean
A genuine NOS watch is one that was made years ago, never sold to a customer, and never worn. It should sit in pristine condition in its original packaging, with stickers still on the caseback, the original warranty card unfilled (or filled but still dated to the period), instruction booklets, hangtags, and the original retailer's seal. The watch will likely need a service before wearing (oils dry over time even if a watch is never used), but the cosmetic condition should be indistinguishable from "fresh from the factory in 1995", or whatever the production date was.
Why it matters
For collectors, NOS pieces are time capsules. A NOS Rolex Sea-Dweller from 1985 has the original tritium lume (which still glows), the original bracelet without polishing, the unfaded matte dial, the original warranty paper showing the period dealer stamp, and the inner cardboard box with no creases. The watch is worth a meaningful premium over even an excellent pre-owned example because everything that wears with use is unworn. For brands' modern reissues, this is the reference point: when AP launches a new "Heritage" piece, NOS originals are the benchmark for "is this faithful?".
Why the word is abused
The word "NOS" carries a price premium of 30-100% over normal pre-owned. This creates strong incentive to call any minty piece "NOS". A watch that has been worn for a few hours, polished once, fitted with a service dial, kept in a drawer for ten years, and now resold may end up listed as NOS. None of these are NOS. Dealers will sometimes use phrases like "NOS-condition", "near-NOS", or "appears NOS" to wiggle around the word; treat all of these as not NOS. True NOS watches almost always come with: factory stickers still on the caseback, factory seal still on the bracelet, unfilled or period-stamped warranty card, all the original packaging materials.
What to inspect
Six things. Caseback stickers: factory protective film should be present and unbroken; if removed, the watch was either delivered to a customer or shop-handled. Bracelet links: a NOS watch usually still has all bracelet links from the factory, never removed for sizing. Crown/case-edge wear: under loupe, brand-new cases show machined-fresh edges; even gentle wear over a few months puts microscopic round-over on edges. Caseback engraving: should match the production year of the case. Warranty card and papers: dated and stamped to the original retailer at original sale; if blank, look for the matching dealer/distributor records. Movement age: a watchmaker can date the movement by serial; if the movement runs 1985 but the case is 1990, you have a parts swap.
"NOS" is not the same as "Like New"
A "Like New" or "Mint" watch can be lightly worn, recently polished, recently serviced, refreshed with a service dial, and still look essentially perfect. NOS is a specific, narrower claim: never sold, never worn, original everything. The price difference between an excellent pre-owned and a NOS is large; the price difference between a "Like New" pre-owned and an honest pre-owned is much smaller. If the seller cannot produce factory stickers and original packaging, treat the listing as Mint pre-owned, not NOS.
Should you pay the premium?
For a long-term collector chasing a specific reference, a genuine NOS piece is worth the premium because the watch will appreciate faster than a worn equivalent. For a daily wearer, NOS is a bad buy: you will wear out the cosmetic premium within months, and the original value gap closes. The grey area: "NOS-grade pre-owned" with full kit and almost-no wear, often available at 70-80% of true NOS price, is an excellent value if you trust the seller. See also: full set vs naked and should I buy pre-owned?