Definition: a ganache or chocolate coating poured at just the right temperature so it runs a little way down the sides of a cake and sets.
A drip cake gets its look from controlled melting. You make a loose ganache, let it cool tojust pourable, then spoon it around the top edge of a well-chilled, iced cake so it slides partway down and stops. Temperature is everything: too warm and it races to the board in thin streaks; too cool and it won’t move at all. Chilling the cake first helps the drip set crisp against the cold buttercream.
In practice: test one drip on the edge first — adjust the ganache’s temperature until it stops halfway.
Related:ganache,crumb coat.