Index

The word "index" has a very large number of completely different meanings in mathematics. Most commonly, it is used in the context of an index set, where it means a quantity which can take on a set of values and is used to designate one out of a number of possible values associated with this value. For example, the subscript in the symbol could be called the index of .

In a radical , the quantity is called the index.

The word index has a special meaning in economics, where it refers to a single quantity used to quantify the "average" value of a possibly complicated set of quantities. In this context, it is sometimes called an index number.

In topology, index theory refers to the study of topological invariants of manifolds.