Volatility
Volatility measures how much a price swings over a period. A volatile market moves hard and fast, in either direction.
Volatility says nothing about direction, only about the size of the moves. Bitcoin is more volatile than gold, gold more volatile than EUR/USD, and GBP/JPY more volatile than EUR/CHF.
It can be measured in several ways: the standard deviation of returns, the ATR (average candle range), or implied volatility derived from option prices, such as the VIX on the S&P 500.
For you, the consequence is concrete: the more volatile a market, the wider your stop must be to avoid being hit by noise, and the smaller your position must be to keep the same risk in money.