Volatility
How much and how fast prices move.
Volatility describes how sharply an investment's price swings up and down. More volatility means a bumpier ride.
Volatility and DCA
Volatility is uncomfortable, but it is also what makes dollar-cost averaging effective: big swings mean your fixed amount buys many more shares at the lows.
Bitcoin is a good example. It has fallen by more than 70% from a peak more than once, then gone on to new highs. Steady buyers rode the swings instead of trying to dodge them.