: the type of a star described primarily according to its surface temperature by means of alphabetic categories (such as O, B, A, F, G, K, and M), decimal subdivisions of the categories, and sometimes symbols indicating special characteristics (such as e for stars with bright emission lines, d for dwarfs, and g for giants)
Our Sun is classified as a spectral type G2.
Note:
Historically, these classes were based on the spectral lines of stars as observed by astronomers. Over time the classes were rearranged according to temperature instead of spectrum, taking them out of their former alphabetic order, but scientists kept using the term "spectral" to describe the system.
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Merriam-Webster unabridged
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