Bear market
A fall of 20% or more from a peak.
A bear market is when prices fall 20% or more from their recent high, usually alongside gloomy news and worried investors.
How often they happen
The S&P 500 has had many bear markets, including about 57% from 2007 to 2009 and about 34% in a few weeks in early 2020. Every one so far has eventually been followed by new highs, though recovery has sometimes taken years.
Why DCA investors care
Bear markets are where steady buying earns its keep. The same $100 buys far more shares when prices are down 30%, and those cheap shares do the heavy lifting in the recovery.