What are major and minor keys that share the same key signature called?

The terms used to describe major and minor keys that share the same key signature are known as relative major and minor keys. This relationship is significant in music theory because it highlights the connection between the two types of scales and their respective tonal centers.

In Western music, each major key has a corresponding minor key that is located a minor third below it. For example, the key of C major shares its key signature (no sharps or flats) with A minor. Both keys utilize the same set of pitches, which allows composers and musicians to transition smoothly between the two keys, creating a rich harmonic landscape.

The concept of parallel major and minor keys refers to keys that share the same tonic note but differ in terms of their key signatures. Enharmonic keys are keys that sound the same but are spelled differently, such as G♯ major and A♭ major. Chromatic scales, on the other hand, consist of a series of pitches that are a half step apart and do not pertain to the relationship between major and minor keys sharing a key signature. Thus, relative major and minor keys serve as a fundamental aspect of tonality and harmony in music, making this choice the most appropriate answer.