What is the main sequence on the spectrum-luminosity diagram: the strip along which the stars evolve, or the locus of points

What is the main sequence on the spectrum-luminosity diagram: the strip along which the stars evolve, or the locus of points in which the stars spend most of their time?

The main sequence contains stars with thermonuclear reactions in the center. This state of the star turns out to be quite long, so the main sequence is the locus of points on the luminosity-temperature plane in which stars spend most of their life.

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