Non-denominated postage

Non-denominated postage is a postage stamp intended to meet a certain postage rate, but printed without the denomination, the price for that rate. They may retain full validity for the intended rate, regardless of later rate changes, or they may retain validity only for the original purchase price. In many English-speaking countries, it is called non-value indicator or non-value indicated (NVI) postage. Introduced to reduce the cost of printing large issues of low-value stamps to "top-up" old issues, NVI stamps are used in many countries.