U use letters to convey meaning and a bunch of l-e-t-t-e-r-s in a row creates a word with a bunch of mean-ing.
R you able to NOT see a pink elephant in your mind? "Pink Elephant" is a phrase that utilizes individual symbols to create an image that comes from your unconscious mind.
The word "Id" is German, and literally means "it." Sig. Freud did not want to define that part of your mind because "Green Ideas" do "Sleep Furiously" in it. That is your desires come from that part of your unconscious mind--"what do you dream about?"