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Market Structure

ETF (Exchange-Traded Fund)

A fund that trades on an exchange like a stock, holding a basket of assets such as stocks, bonds, or commodities. SPY and QQQ are ETFs.

What is an ETF?

An ETF (Exchange-Traded Fund) is a fund that holds a collection of assets and trades on a stock exchange just like a regular stock. When you buy one share of an ETF, you get exposure to everything it holds. You can buy and sell ETFs throughout the trading day at market price, unlike mutual funds which only trade once per day at closing price.

Common ETFs traders should know

  • SPY: tracks the S&P 500 (500 largest US companies). The most traded security in the world
  • QQQ: tracks the Nasdaq-100 (100 largest non-financial Nasdaq companies). Heavy in tech
  • IWM: tracks the Russell 2000 (2,000 small-cap US companies)
  • DIA: tracks the Dow Jones Industrial Average (30 blue-chip companies)
  • GLD: tracks the price of gold
  • TLT: tracks long-term US Treasury bonds
  • XLF, XLE, XLK: sector ETFs (financials, energy, technology)

Why traders use ETFs

  • Market direction: instead of picking individual stocks, trade SPY or QQQ to bet on the overall market direction
  • Sector plays: sector ETFs let you trade an entire industry (energy, tech, healthcare) without picking a single stock
  • Liquidity: major ETFs like SPY have extremely tight spreads and massive volume, making them easy to enter and exit
  • Hedging: short SPY or buy inverse ETFs to hedge a long stock portfolio during uncertain markets
  • Benchmarking: compare your trading performance against SPY to see if you are actually beating the market

ETFs vs individual stocks for day trading

  • Lower volatility: ETFs move less than individual stocks because they hold many positions, so intraday swings are smaller
  • More predictable: index ETFs follow macro trends rather than single-company catalysts
  • Options friendly: SPY and QQQ have the most liquid options markets in the world
If someone says "the market is up 1% today," they usually mean SPY is up 1%. SPY is the default benchmark for the US stock market.

Related Terms

Dow Jones Industrial Average

An index of 30 large blue-chip US companies. The oldest and most widely quoted market index, though many traders consider the S&P 500 more representative.

Index

A measurement of a section of the stock market. The S&P 500, Nasdaq Composite, and Dow Jones are the three most watched indexes.

Mutual Fund

A pooled investment fund managed by a professional that buys a portfolio of stocks, bonds, or other assets. Investors buy shares of the fund, not the individual holdings.

QQQ

The Invesco QQQ ETF, tracking the 100 largest non-financial companies on the Nasdaq. Heavily weighted toward tech giants like Apple, Microsoft, Nvidia, and Amazon.

SPY

The SPDR S&P 500 ETF. The most traded security in the world, tracking the 500 largest US companies. When traders say "the market," they usually mean SPY.

Sector Rotation

When money flows from one market sector to another as economic conditions change or investors shift risk appetite.