An index fund is a type of mutual fund with a portfolio constructed to match or track the components of a market index. 

An index mutual fund is said to provide broad market exposure, low operating expenses and low portfolio turnover.

Indexing is a passive form of fund management that has been successful in outperforming most actively managed mutual funds. 

Example:
The BitFund Balanced 10 Portfolio tracks the top 10 cryptocurrencies by market capitalisation similarly to the S&P500 stock market index which tracks the market capitalizations of 500 largest companies.

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