Trading glossaryReviewed 16 July 2026
Definition
An index is a rules-based statistical measure that tracks the performance of a defined group of instruments, markets, or economic observations.
In market context
Index methodology determines eligibility, weighting, rebalancing, corporate-action treatment, and calculation, so two indices covering similar markets can behave differently. An index itself is generally a measure rather than an investable account asset; funds and derivatives seek to provide related exposure and introduce their own costs and tracking differences. Past index performance excludes some practical constraints and does not predict future returns.
Source
Use the primary source for fuller regulatory or market context.