Index fund
What it means
A fund that holds all (or a representative sample) of the companies in a market index — like the S&P 500 — instead of a manager picking individual stocks. It moves with the market rather than trying to beat it.
Why it matters
Low fees and broad diversification in one purchase make index funds the standard "boring base" recommended across nearly every guide on this site.
A worked example
An index fund tracking the S&P 500 holds around 500 companies. If one of them collapses entirely, it was perhaps 0.1% to 7% of the fund depending on its size — a real loss, but not a catastrophic one.
Compare that with holding five individual stocks. One going to zero costs you 20% of the portfolio. The fund did not make better predictions; it simply spread the consequence of being wrong across enough companies that no single mistake is decisive.
What people get wrong
"Index fund" gets read as "safe," and it does not mean that. An index fund holds the market, so it falls when the market falls — including the years it falls a great deal. What diversification removes is the risk of any single company ruining you. It does nothing about the risk of the whole market declining at once, and no fund structure can.
The related error is buying several index funds and assuming that adds diversification. If they all track large US companies, you may own the same handful of businesses several times over.
How this works in Latin America
From most of Latin America, buying a broad global or US index fund usually means going through a local broker that offers international listings — Mexico's SIC on the BMV and Brazil's BDR structure on B3 both exist for this — or through an international brokerage that accepts residents of your country.
The consequence people underestimate is currency. A fund priced in dollars held by someone who earns and spends in pesos or reais has two moving parts: what the fund does, and what the exchange rate does. In a year when the market rises 10% and your currency strengthens 10% against the dollar, the gain in local terms is close to nothing. That works in both directions, and it is a genuine part of the risk rather than a footnote.