Exchange-traded funds (ETFs) can be a tax-efficient, low-cost investing option for investors looking for a well-diversified portfolio. Learn more about ETFs including what they are and how they work.

So, a bitcoin futures ETF is an exchange-traded fund that holds bitcoin futures contracts and sells shares of the fund to investors. These shares are bought and sold on a mainstream exchange.

However, an inverse ETF can also be leveraged, meaning it can seek 2x or 3x the expected performance of the index or asset it tracks. That's where things get especially risky.

Passive fixed-income ETFs use an index to define their holdings. These funds have low expense ratios and should perform in line with their underlying index.

Spot ethereum ETFs finally reach the US stock exchange. Should you invest? ... meaning the ETF will need to bear the costs of buying and selling ether when ETF shares are created or redeemed.

Shares of leveraged ETFs are traded in the open market like a stock. Some leveraged ETFs are not heavily traded, meaning that your ability to buy or sell shares in a leveraged fund may be constrained.