What do we call the relationship between major and minor keys that share the same key signature?

The relationship between major and minor keys that share the same key signature is known as relative major and minor. This term describes pairs of keys that are positioned a minor third apart from each other. For instance, C major and A minor both have no sharps or flats in their key signature, illustrating this relationship. In musical practice, the relative minor key is often derived from the sixth degree of its relative major scale.

Understanding this concept is crucial for composers and musicians as it helps with key modulation, composition, and improvisation. Application of this knowledge enables musicians to create complementary melodies, harmonies, and transitions between different musical sections effectively.