subindex

1. Mathematics. A subscript.
2. pl. -dic·es or -dex·es. An index of measurement based on relatively few variables, especially a trade index based on the performance of a particular group or type of stocks.

A group of securities that is part of an index but is also tracked separately as a smaller, separate index.

Investopedia Says:
A software index, for example, would be a sub-index of a computer index.

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Get to know the most important market indices and the pros and cons of investing in them. Index Investing

An index representing a sector of a larger index. For example, the Nasdaq Telecommunications Index is one of 11 subindexes of the Nasdaq Composite Index. See also Stock Indices and Averages.