平行大小调（俄文：Параллельные тональности），或称关系大小调（英文：relative key）。

平行调指的是两个主音不同、音列相同的调的关系。

例如C自然大调的平行小调为a自然小调。

平行调一词从俄文（Параллельные тональности）翻译而来，但英文中的parallel key（直译为平行的调）指的是同主音调。这导致了在中文和英文乐理书籍翻译中的一些混淆。

In music, relative keys are the major and minor scales that have the same key signatures. A pair of major and minor scales sharing the same key signature are said to be in a relative relationship. The relative minor of a particular major key, or the relative major of a minor key, is the key which has the same key signature but a different tonic; this is as opposed to parallel minor or major, which shares the same tonic. Relative keys are closely related keys, the keys between which most modulations occur, in that they differ by no more than one accidental (none in the case of relative keys).