Laspeyres Index

Index Number
Understanding index numbers as indicators showing the relative size of variables based on a chosen base value, typically representing averages or aggregates across sectors.
Base Period - Definition and Meaning
The period whose data are identified with an index of 100 (or sometimes 1) for the construction of an index number.
Laspeyres Index
An economic measure used to calculate the price change in a specific basket of goods over time using a fixed base period.
Price Index
An index number representing the average of prices of goods in a given category.