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Predicting the actions of human being is very difficult. The market "crashes" when 2 people throw in the towel. One of those groups is the aggregate of retail+institutional buyers. The other group is market makers. When neither group is willing to bid the price, then that price decreases. When neither group is willing over an extended period of time(say, an hour), we have a "market crash". It's a very hyperbolic way of saying no one is willing to buy, but others are still willing to sell. In that state, the price retreats as buy-side liquidity is consumed, and continues retreating until buy-side liquidity is equal to sell volume. Once buy-side liquidity is in excess of sell volume, then the price moves up.

tldr; "crash" is used to describe a very natural condition, caused entirely by the emotions of human beings.