NIB means in the same condition as when the gun left the factory, with accompanying box, literature, and accessories. This is important to note, as older boxes may have substantial value in themselves. Purists will want the box to be the original box which that particular gun was shipped in (serial number was often penciled on the bottom or marked on the end of the box by the factory).
As to the condition of the gun itself, the gun must be unfired and unused. Comparable terms expressing the same gun condition when not accompanied by box might include "AS NEW," "MINT," "PERFECT," or 100%." Even if the gun has never been fired, if the action has been worked to the extent that wear is visible, the value may be less that "NIB" or "AS NEW" to a collector. For example, the faint drag line that appears on the cylinder of a revolver that has been dry-fired a few times will reduce the value to less than "AS NEW" for a condition purist on an out of production revolver. This sort of general shop-wear to an otherwise new, current production gun will not matter to a buyer purchasing the gun to shoot. It rapidly becomes more important to a condition collector who wants a truly pristine example of an out-of-production piece.
Generally this condition is seldom found in older antique guns, but an older antique gun that is NIB or AS NEW will bring substantial premium over antique Excellent condition - sometimes bringing double or more what the same model would bring in EXCELLENT condition.
