Before revision: Ego depletion is the idea that self-control or willpower draws upon a limited pool of mental resources that can be used up (with the word "ego" used in the psychoanalytic sense rather than the colloquial sense).
After revision: Ego depletion is the idea that self-control or willpower draws upon conscious mental resources (libido) that can be taxed to exhaustion when in constant use with no reprieve (with the word "ego" used in the psychoanalytic sense rather than the colloquial sense).