Volatility

What it is

Volatility measures how much a series moves around its average — usually the standard deviation of returns.

Why it is not the same as risk

Volatility treats up-moves and down-moves the same. Risk is about the down part. A strategy that swings wildly upward is volatile but not, in that moment, risky.

Volatility is nonetheless the raw material of most risk measures — Sharpe, position sizing, margin — which is why understating it matters.

How it gets understated

Way	Why it hides risk
Smoothed pricing	Formula-priced assets move less on paper than in reality
Short windows	A calm stretch looks permanently calm
Survivorship	Failed names (which were volatile) are missing entirely

How to check

Ask what the volatility estimate used and over what window. A volatility number without its method is not a measurement.