Have a video.
The Id is a part of Sigmund Freud's hypothesis on the structure of personality. There are three parts to the structure: The Ego, which is the rational part of a person's mind; the Superego, which is a person's sense of right and wrong; and there is the Id, a person's basic instincts and impulses.
The Id focuses on pleasure, on what a person wants to do for themselves. The libido, or sex drive, is the most commonly known drive of the Id, though there are many others.
Rocky Horror Picture Show is basically a 90 minute long explanation of this. One of the most prominent lines in the film/play is "Give yourself over to absolute pleasure," and the whole movie is pretty much one giant singalong orgy, so I thought posting a song from it would be a nice example.