What is an ETF?
An ETF is a fund you buy and sell like a share. That one sentence hides most of what matters: what you actually own, what it costs, and why holding a broad fund is not the same as being diversified.
What an ETF actually is
An exchange-traded fund holds a basket of assets — shares, bonds, commodities — and issues units that trade on an exchange. Buying one unit gives you proportional exposure to everything in the basket, without buying each holding separately.
Most are index funds: rather than picking holdings, they track a published index and hold roughly what it specifies. That keeps costs low, and it means the fund will follow the index down as faithfully as up. Tracking an index is not a defensive feature.
ETF units versus individual shares
| A single company's shares | An index ETF | |
|---|---|---|
| What you own | A stake in one company | A unit in a fund that holds many |
| Company-specific risk | Concentrated in that one business | Spread across the holdings |
| Market-wide risk | Present | Equally present |
| Ongoing cost | None beyond dealing costs | An annual expense ratio |
| Shareholder votes | Normally yours | Normally exercised by the fund |
| Income | Dividends, if paid | Distributed or reinvested by the fund |
The row people skip is market-wide risk. Spreading across five hundred companies removes the risk that one of them fails. It does nothing about the risk that the whole market falls, and in a broad selloff most holdings fall together.
Diversified is not the same as evenly spread
Most large equity indices are weighted by market value, so the biggest companies take the largest share. A fund tracking a major index can therefore have a substantial portion of its value in its top handful of holdings, often concentrated in one sector.
That is not a flaw, but it does mean "I hold an index fund" and "my exposure is evenly spread" are different statements. The fund's own factsheet lists its top holdings and their weights — that document is the authority, not a general description like this one.
What to check before researching any ETF
- What index does it track, and what are that index's rules for inclusion?
- Top holdings and their weights — how concentrated is it really?
- Expense ratio — the annual cost, deducted from the fund's value.
- How it holds its assets — physically, or through derivatives (synthetic replication)? The latter introduces counterparty risk.
- Distributions — does it pay income out or reinvest it?
- Size and trading volume — very small or thinly traded funds can be harder to exit.
- Is it leveraged or inverse? These reset daily and are designed for short holding periods. Over longer periods their returns can diverge sharply from a simple multiple of the index.
Same ticker, different instrument. Holding units of an index ETF, buying short-dated options on it, and trading a leveraged product that uses its name are three different things with three different risk profiles. Check which one you are actually looking at before comparing them.
An ETF can still lose money
A broad fund can fall a long way and stay below a previous high for years. Diversification across companies reduces the chance that one failure wipes you out; it does not promise a positive return over any particular period, and no fund does.
Reading the source
Every ETF publishes a prospectus and a factsheet setting out its objective, holdings, costs and risks. For SPY, one of the most widely held equity ETFs, that is published by State Street: SPY's objective, holdings and risk disclosure. Issuers change terms, so treat the issuer's current document as authoritative.
Look at an ETF chart in the research deskNext
What moves the price of gold covers a market that behaves differently from equities, and paper trading covers practising before any money is involved.