noun
: a number used to indicate change in magnitude (as of cost, price, or volume of production) as compared with the magnitude at some specified time usually taken as 100
if the cost of an item in 1930 was one and one half as much as its cost in 1913, its index number, relative to 1913, was 150
relative index numbers representing changes in price level of the particular type of asset being considered would be used for the purpose of converting fixed assets to current dollar values — Accountants Digest
— used especially in statistics