AI Summary
An index, in the context of financial markets, is a statistical measure of the performance of a portfolio of stocks or other securities, used to represent a specific market or segment. Recently, the S&P 500 index has been prominent in news due to the inclusion of Datadog (DDOG), which caused its stock to soar, and the concurrent exit of Juniper (JNPR); these events occur while the S&P 500 itself approaches all-time high levels, prompting discussions about market investment strategies.