In music, notes that are sharped, flatted, or naturalized outside the key signature; plural of accidental.
From accidental + -s (plural marker). In music, these notes are 'accidental' to the key because they don't belong to the standard scale.
Accidentals in music are like rule-breakers—a composer uses them to create tension or surprise by adding notes that don't 'belong' to the key, making the listener feel something is off in exactly the right way.
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