Final answer:
Portfolio management that uses a market index as a benchmark for performance is classified as a passive investment strategy, typically exemplified by index funds.
Step-by-step explanation:
In the context of portfolio management, if a mutual fund or any investment portfolio seeks to mimic the market's overall performance using a market index as a benchmark, this strategy is known as a passive investment strategy. Unlike active management, which attempts to outperform the market through selecting individual investments, passive management involves holding a diversified mix of assets in proportions similar to a market index. An index fund is a common example of a passive investment vehicle that aims to replicate the movements of an index of a specific financial market, or a mix of markets.