在西方文化的古典音乐里，七度是一个横跨七个五线谱位置（参见音程#音级）的音程。而小七度是两个常见七度之一。小七度表示它是那两个中较小的一个：小七度横跨十个半音，而大七度横跨十一个。例如，从A音到G音的音程是小七度，因为G音比A音高十个半音，而且从A音到G音有七个五线谱位置。减和增七度也是横跨七个五线谱位置，但减七度横跨九个半音，增七度横跨十二个半音。

小七度比大七度在旋律中更常见。最广为人知的例子是星际争霸战的主题曲的开头的两个音。还有一个例子就是梦断城西的Somewhere的「There's a place for us」的头两个字。

In classical music from Western culture, a seventh is a musical interval encompassing seven staff positions, and the minor seventh is one of two commonly occurring sevenths. It is qualified as minor because it is the smaller of the two: the minor seventh spans ten semitones, the major seventh eleven. For example, the interval from A to G is a minor seventh, as the note G lies ten semitones above A, and there are seven staff positions from A to G. Diminished and augmented sevenths span the same number of staff positions, but consist of a different number of semitones (nine and twelve).