Spectrum
A sound split into its frequencies, showing how loud each one is at that moment.
See it in Audio visualizer. Press Microphone, pick Spectrum and hum a low note, then a high one.
In plain words
Most sounds are many tones mixed together. A spectrum pulls the mix apart and shows each tone on its own. Low sounds sit on the left, high ones on the right, and each bar is as tall as that part is loud. A bass drum lights up the left side, and a cymbal lights up the right. Music visualisers redraw the spectrum many times a second.