ZBLL

ZBLL (short for Zborowski-Bruchem Last Layer) is a step of a method which involves solving the entire last layer in one step, assuming that the edges are already oriented. This is part of the ZB method, but it can be useful for any other method which leaves the edges of the last layer oriented after F2L is solved (such as the Petrus method).

ZBLL indeed sounds like a very useful step to learn, but the main reason that it is not in wide use is that it involves a massive 177 algorithms (counting inverses and mirrors are the same), or a total of 493 cases. Only a handful of people have ever learned this step in its entirety. If you wish to learn it, it is useful to start by learning either OCLL/PLL or COLL/EPLL, so that you will always be able to finish the cube relatively quickly even if you do not yet know the ZBLL case.