A #ETF (Exchange-Traded Fund, or Exchange-Traded Investment Fund) is a type of investment fund that is traded on a stock exchange, just like stocks.

An ETF is an investment vehicle that allows investors to access a diversified portfolio of assets, such as stocks, bonds, commodities, currencies, etc., through a single investment.

ETFs are characterized by:

1. Diversification: ETFs offer a diversified portfolio of assets, which can help reduce risk.

2. Flexibility: ETFs can be bought and sold at any time during the day, just like stocks.

3. Transparency: ETFs publish their asset portfolio daily, allowing investors to know exactly what assets they own.

4. Low costs: ETFs usually have lower management costs than traditional mutual funds.

5. Access to markets and assets: ETFs offer access to markets and assets that may be difficult to access otherwise, such as emerging markets or commodities.

There are different types of ETFs, such as:

- Equity ETFs: which track a stock index, such as the S&P 500.

- Bond ETFs: which track a bond index, such as the U.S. Treasury bond index.

- Commodity ETFs: which track a commodity index, such as gold or oil.

- Currency ETFs: which track a currency index, such as the U.S. dollar currency index.

In summary, ETFs are a flexible and diversified investment tool that provides access to a wide range of assets and markets, with low costs and transparency.