> You can see a lot of repetition in the vertical direction, but these are probably redundant resonances. They don’t add any more information, so we should only look at the base frequencies.
In the context of audio, these are just called "overtones", and the "base frequency" is the "fundamental".
The amplitudes of the overtones are what give an instrument its characteristic timbre. It's what makes a flute sound different from, say, a sax, when they are both playing the same note.