Base period
The period, such as year or a month, with which all other values in a series are compared.
Index number
An indicator showing the relative value of one number to another from a base of 100. It is often used to present an average of a number of statistics.
Nominal values
Values unadjusted for the effects of inflation (i.e. values at current prices.)
Real values
Values adjusted for inflation (i.e. values at constant price.)