Pâte Fermentée is a French term that refers to a dough that is made before the bulk of the main bread dough is put together and allowed to mature or ‘ferment‘.
By preparing a portion ahead of time, it can be allowed to ferment overnight (or however long) in a cool space (slowing yeast activity) where it develops a lot of great flavour that would not be available in a shorter rest time. The dough is then added to the rest of the bread’s ingredients and presto, your “new” dough gets a tremendous flavour boost.
In a bakery setting, a large amount of this dough would be made regularly and a small portion of it would go into, say, baguettes, another portion into kaisers, etc. This is why the pâte is very basic – it would be used throughout the day to make whatever bread was on the menu.
At home, you still want the fermentation/development that occurs but would normally just make enough for your next bake.
In The Bread Baker’s Apprentice, this shortcut is used a fair bit. It’s a very simple, lean dough.