在西方文化的古典音乐中，一个小三度是一个横跨三个半音的音程。在五线谱中，小三度横跨三个五线谱位置。而小三度（ 播放）是两个常见的三度（大三度和小三度）的其中一个。它之所以被称为小三度是因为它是两个中最小的，大三度比小三度多跨越一个半度。例如，从A到C的音程是一个小三度，因为C在A的三个半音之上，而且从A到C有三个五线谱位置。减三度和增三度也是跨越三个五线谱位置，但半音的数量不同(减三度为两个半音，增三度为五个)。

小三度是泛音列中第五个到第六个中的音程，而且是第十六个到第十九个泛音的音程。

In the music theory of Western culture, a minor third is a musical interval that encompasses three half steps, or semitones. Staff notation represents the minor third as encompassing three staff positions (see: interval number). The minor third is one of two commonly occurring thirds. It is called minor because it is the smaller of the two: the major third spans an additional semitone. For example, the interval from A to C is a minor third, as the note C lies three semitones above A, and (coincidentally) there are three staff positions from A to C. Diminished and augmented thirds span the same number of staff positions, but consist of a different number of semitones (two and five). The minor third is a skip melodically.