Volatility is a measure of how much a data series fluctuates over time. In finance, an asset like a Treasury has low volatility, while meme stocks are highly volatile. In general, investors prefer volatility in order to reduce risk. For example, it is harder to get margin to trade on highly volatile securities since you might have to place a large amount of money as collateral in case the price of the security plummets. In contrast, collateral requirements for highly stable assets will be lower.