异名同音（或异符同音）在音乐理论中，是指音名不同而音高相同，除了G♯和A♭的组合外，其他组合都是三个一组。这是平均律初出现时产生的概念，巴洛克时期以后，异名同音被广泛使用。到了浪漫主义音乐时期，则完全普及。

（□是钢琴白键，■是黑键。）

In modern musical notation and tuning, an enharmonic equivalent is a note, interval, or key signature that is equivalent to some other note, interval, or key signature but "spelled", or named differently. Thus, the enharmonic spelling of a written note, interval, or chord is an alternative way to write that note, interval, or chord. For example, in twelve-tone equal temperament (the currently predominant system of musical tuning in Western music), the notes C♯ and D♭ are enharmonic (or enharmonically equivalent) notes. Namely, they are the same key on a keyboard, and thus they are identical in pitch, although they have different names and different roles in harmony and chord progressions.