A 45 is a 45 rpm record. Not rpm as in the package manager, but as in revolutions per minute; 45 rpm was how fast it spun around a turntable. There was music on it, only about 3-5 minutes on each side (you had to get up and turn it over to hear both sides, but you could also stack'em ad infinitum if your player could handle that). You could only hear music if the stylus was attached to the spinning vinyl - unless you're like John Cage, diggin' the sound of the motor.