ETF is an abbreviation for Exchange Traded Fund. These are funds, traded on an exchange (like an investment company), that issue and redeem shares to match supply and demand (like a <a href="https://quoteddata.com/glossary/zero-discount-mechanism-zero-discount-policy/">zero discount mechanism</a>), and generally track an index which could be based on a range different asset classes. The manufacturers of ETFs have become more inventive over the years and they now offer funds, for example, which are net <a href="https://quoteddata.com/glossary/net-short/">short</a> of the market, or <a href="https://quoteddata.com/glossary/gearing/">geared</a>, or based on a subset of the market selected on <a href="https://quoteddata.com/glossary/qualitative/">qualitative</a> grounds. The more complex these funds get, the more wary you should be of them. If you are not completely sure how these funds will perform in any given scenario, it might be best to ask an adviser before investing in them.