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A classic bargraph style spectrum analyzer.
Spectrum analyzers are devices that displays how much energy an input waveform has at different wavelengths. The classic spectrum analyzer used a narrow bandpass filter that swept through the audio range, graphing the level of signal that passed through the filter at different frequencies. These devices were accurate but slow; they were not capable of accurately measuring a changing waveform. In the late 1970s, the first "real-time" analyzers were developed, using banks of bandpass filters tuned at specific intervals (typically one octave or 1/3 octave apart) and using an array of indicator lights to display the results in bar-graph style.
Most current spectral analyzers use Fast Fourier Transform to perform the analysis and are often logarithmically scaled in frequency (but FFTs are not) but there's other methods like constant-Q transform and variable-Q transform and more commonly IIR filter bank, which has logarithmic frequency resolution.