A set of
securities in an
index whose performance is also tracked independent of the other securities in the index. An index may divide itself into subindicies for the different sectors it tracks. For example, the S&P 500 contains 10 subindices representing various sectors of the
economy, such as energy or health care companies. A subindex may also be created for subsets of a specific sector. Given an index of the energy sector, for example, one may create subindices of oil companies and alternative energy companies.