The moment you turn 18, you can open a brokerage account and start investing. Most people don't — not because they can't afford to, but because the terminology feels like a foreign language. That barrier is removable.

These 10 terms are the foundation. Master them and every conversation about investing, every article you read, every decision you make will make more sense.

Term 01
Stock

A share of ownership in a company. When you buy a stock, you own a small piece of that business — including a claim on its future profits and assets.

Example: If Apple has 15 billion shares outstanding and you own 10, you own roughly 0.000000067% of Apple.
Term 02
Index fund

A fund that tracks a market index — like the S&P 500 — by holding all (or most) of the stocks in that index. Instead of picking individual winners, you own a slice of the whole market.

Example: The Vanguard S&P 500 ETF (VOO) holds all 500 companies in the S&P 500. One share gives you exposure to Apple, Microsoft, Amazon, and 497 others.
Term 03
Compound interest

Earning interest on your interest. The longer your money stays invested, the faster it grows — because each year's gains become the base for next year's gains.

Example: $1,000 invested at 8% annual return becomes $2,159 in 10 years, $4,661 in 20 years, and $10,063 in 30 years — without adding a single dollar.
Term 04
Expense ratio

The annual fee a fund charges, expressed as a percentage of your investment. A 1% expense ratio costs $10/year on a $1,000 investment. Index funds typically charge 0.03%–0.20%.

Example: Over 30 years, a 1% expense ratio costs you roughly 25% of your ending balance compared to a 0.05% fund. On $100,000, that's about $100,000 lost to fees.
Term 05
Dividend

A portion of a company's profits paid to shareholders, usually quarterly. Not all companies pay dividends — growth companies typically reinvest profits instead.

Example: If you own 100 shares of Coca-Cola and the quarterly dividend is $0.46/share, you receive $46 every quarter — $184/year — just for holding the stock.
Term 06
Diversification

Spreading investments across different assets, sectors, or geographies so that one bad investment doesn't destroy your portfolio. The core principle of risk management.

Example: Owning 500 stocks via an index fund means one company going bankrupt affects less than 0.2% of your portfolio.
Term 07
Risk tolerance

Your personal capacity to handle investment losses without making panic decisions. Higher risk tolerance = comfortable holding through market downturns. Lower = prefer stable, lower-return investments.

Example: In 2020, the S&P 500 dropped 34% in 33 days. Investors with high risk tolerance held or bought more. Those with low tolerance sold — and missed the recovery.
Term 08
Roth IRA

A retirement account where you contribute after-tax money, but all future growth and withdrawals are tax-free. At 18, opening a Roth IRA is one of the highest-leverage financial decisions you can make.

Example: $6,000 contributed at age 18, left untouched until 65, grows to ~$200,000 tax-free at 8% average annual return.
Term 09
ETF (Exchange-Traded Fund)

Like an index fund, but traded on a stock exchange throughout the day. ETFs combine the diversification of a mutual fund with the flexibility of a stock.

Example: VOO (Vanguard S&P 500 ETF) trades on the NYSE. You can buy 1 share for ~$500 and own proportional stakes in 500 companies instantly.
Term 10
Dollar-cost averaging

Investing a fixed amount at regular intervals regardless of market conditions — rather than trying to time the market. Reduces the impact of volatility over time.

Example: Investing $100/month in an S&P 500 ETF every month for 10 years, regardless of market conditions, historically outperforms most attempts to "buy the dip."

Practice these 10 terms with an interactive puzzle — find each word, then click it to review the definition.

Play: Stock Market Terms →

The one thing most 18-year-olds get wrong

They wait. The average American starts seriously thinking about investing at age 31 — 13 years after they could have started. Compound interest is ruthlessly time-dependent: $1 invested at 18 is worth roughly 4× more at retirement than $1 invested at 35.

The vocabulary in this list is the entry point. Once these 10 terms feel familiar, the next step — opening a Roth IRA and buying a low-cost index fund — becomes obvious rather than intimidating.