You know that gizmo that shows a number of vertical lines (as few as three, as many as several dozen (I guess?)) that audio technicians use? The lines will rise and fall as the music or whatever progresses. What’s it called? And what information do you get from it – as in, how does the second vertical line from the left rising and falling at this time, while the fourth vertical line from the left rises and falls at that time – how does this information help you more fully understand your quarry? And how does it direct you to what to do with it (if you’re in the business of manipulating sound)?
Graphic equalizer, at least the readout for it. Each line represents a frequency. The tech will have a slider for each frequency to adjust the sound.
Slight nitpick: a range or band of frequencies.
The low range frequencies like bass guitar will be on the left, midranges like the human voice in the middle, and highs like cymbals on the far right. The slide controls are pretty much volume controls for the various band widths. The sound mixers can play with it to get the desired range emphasis where they want it at different times throughout a song.
It’s a poor-man’s Spectrum Analyzer.
It could be a single frequency - if you have enough lines and sliders !
More than the Universe could contain 
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We did fine for years with Bass & Treble!
Over in the ham and scanner world, cheap processing and memory has made super wideband RF receivers basically disposable and there are some visualizations possible that used to be pretty much Star Trek-Tron stuff. Broadly called waterfalls, they show all sorts of data with respect to time. That’s been around for a while for audio but it’s a lot harder to sample and remember chunks of signal a meg at a time.
If you’re specifically referring to the LED strips you see being used to monitor the loudness of channels or of specific groups of frequencies on a mixing board and/or its outboard modules, that’s an audio meter. In the past, that’s what the little VU meters were for, modern equipment often uses strips of multicolored LEDs for the same purpose. My board at home uses a combination of VU meters for the stereo mix it’s sending out, and a LCD screen for metering the individual channels.