Buy the dip
Buying after a price drop.
"Buy the dip" means adding money after prices fall, on the idea that you are getting a discount.
The problem with waiting
Buying a dip is great. Waiting for one is the hard part: if prices keep rising, the cash you held back misses the gains, and the dip you finally get may still be above where you could have bought months earlier.
With DCA you buy dips automatically. Your fixed amount buys more shares whenever prices are down, without any waiting or guessing.