An ETF bundles many stocks or bonds into a single fund, but unlike a regular mutual fund it is listed on a stock exchange and its price moves throughout the trading day. You buy and sell ETF units through a demat and trading account exactly as you would a share.
How an ETF differs from a mutual fund
The holdings can be identical. The difference is the wrapper.
A mutual fund is priced once a day. Whatever time you place your order, you get that day's NAV, and you transact with the fund house itself. An ETF trades continuously, so its price moves minute to minute, and you transact with another investor on the exchange rather than with the fund.
That gives ETFs intraday flexibility. You can place limit orders, buy at a specific price, or sell mid-session. It also introduces two frictions a mutual fund does not have: you pay brokerage on each trade, and the market price can drift slightly away from the fund's true underlying value.
Tracking error and the price gap
Two small imperfections are worth understanding before you buy.
Tracking error is the gap between the index's return and the ETF's return. It exists because the fund charges a fee, holds a little cash, and has to trade when the index rebalances. A well-run large ETF keeps this small; a thinly-traded one may not.
The premium or discount is the gap between the ETF's market price and the value of what it actually holds. In a liquid ETF this stays negligible. In an illiquid one, especially during a volatile session, you can pay meaningfully more than the units are worth. Checking the traded volume before buying matters more with ETFs than with mutual funds.
Why the cost is so low
Most ETFs are passive: they mirror an index such as the Nifty 50 rather than employing a manager to pick stocks. No research team means no research budget, which is why the expense ratio on a large index ETF is often a small fraction of what an actively managed fund charges.
That gap looks trivial in one year and decisive over twenty. A difference of one percentage point in annual cost, compounded across a working life, is a large amount of money that stays in your account instead of the fund's.
What you actually own
A Nifty 50 ETF gives you a proportional stake in India's fifty largest listed companies in a single trade. If those companies collectively rise, so does your ETF, minus the fee. If they fall, so does it. You are accepting the market's return rather than trying to beat it, and consistently beating it turns out to be rare.
Beyond equity indices, ETFs exist for gold, for bonds, for international indices, and for narrower themes and sectors. The broad, boring ones are generally the ones worth owning; the narrow thematic ones concentrate risk in exactly the way an ETF is supposed to avoid.
ETF or index fund?
They do the same job through different plumbing, and for most people the index fund is the more practical choice.
An index fund needs no demat account, charges no brokerage, and accepts a SIP. You can automate Rs 2,000 a month and never think about it. An ETF needs a demat and trading account and cannot be automated in the same way, but gives you intraday pricing and often a marginally lower expense ratio.
If you are investing a fixed amount every month and want it hands-off, the index fund wins on convenience. If you already trade, hold a demat account, and are deploying larger sums at once, the ETF's lower running cost starts to matter.
Either way you get instant diversification at a low cost, which is the substance of the decision. The wrapper is a detail.