What is volatility, and what does standard deviation tell me?

Volatility is how much an investment's price bounces around, and standard deviation is the most common way to measure it – a single number summarizing how far returns typically stray from their average. A fund with a high standard deviation swings widely (think individual stocks or emerging markets), while one with a low standard deviation is steadier (think short-term bonds or money market funds). Higher volatility isn't automatically bad: for long-term investors, it's the price of admission for stocks' higher expected returns, and the swings smooth out over decades. It matters most when your time horizon is short, because a volatile asset can be down sharply exactly when you need the money. Think of standard deviation as a measure of the bumpiness of the ride, not the destination. Match the volatility you hold to how soon you'll spend the money.