The relevant phrase in the Michael Cohen indictment referring to Trump was "unindicted co-conspirator". Individual one is how they referred to him. Trump was supposed to be featured much more prominently in the indictment, but the Barr's DOJ intervened on Trump's behalf to minimize his presence in the proceedings, and they went out of their way not to mention him.
They got Michael Cohen for this, and Trump was mentioned in his proceedings as “individual one”.