A 'dub' is a double flip. It just so happens that the cork is the most commonly doubled flip, so 'dub' usually refers to a double cork. However, double mistys, bios, fronts, back, rodeos, etc are all possible.
A dub (dub cork) is when you spin cork, then uncork so that you're spinning normally, then either go corked again, or spin on another axis.
Any number of degrees of rotation is hypothetically possible. The two flips in a double don't have to have the same number of degrees of rotation. So a dub 9 could be a cork 5 then a cork 3, etc: it is the number of distinct flips that makes a double a double.
Or, when two different flips are performed within the same airtime.