Definition of a baneling bust

A "Baneling bust" is when you use a lot of Banelings to breach the enemy's "front door" - the bunch of buildings used at the ramp of the main base to block or hinder the enemy from entering.

Since Banelings do so much damage against buildings, they are very useful for quickly bringing down low-HP buildings commonly used for fortifying this front door - mainly supply depots, bunkers and pylons - and thus opening the way to the opponent's base. This tactic is called the Baneling bust, even if you destroy just some of the buildings composing that "door", not all of them.

The Baneling bust is a lot less useful against front doors made from higher-HP buildings, like gateways or barracks.