Volatility describes the degree to which a value, such as a stock price or an interest rate, changes over a specified time period. High volatility means that the value changes dramatically, usually due to high market uncertainty. Traders thrive on market volatility because it presents many opportunities to earn a profit. Low volatility means values change minimally, as is the case when all news has been priced into the market. Professional investors tend to benefit from low volatility because they are better able to lock in stable returns. The financial markets distinguish between historical volatility and implied volatility. Historical volatility is a measure of volatility based on past price or yield behaviour, while implied volatility is an estimation of future behaviour, implied by the price of an option.