Het means it has the genetic trait for a morph other then itself. Like lets say you breed a 50het albino with a 50 het albino, you will probably get at least 1 albino baby.
To get a het:
Lets say you have 2 100% Albino BP's and you bred them together and the female lays 6 eggs. All 6 eggs hatch and lets say you get 5 albinos and 1 normal. That means that the 1 normal is 50% het for albino. At least I'm pretty sure thats how it works o_O