It can also mean something where you focus on one craft to improve upon it. An example would be investing your time on a relic weapon for a specific class. There's no known information on what kind of specialization it is, or if its restricted to one class.
Though I'd still hope it doesn't disallow for the freedom of crafters being able to access all the recipes; it's just asking for trouble when it comes to balancing crafted equipment and consumables.