Final answer:
The relative minor of C major is A minor. This is determined by counting down three semitones from the tonic of the C major scale, which leads to the key of A minor.
Step-by-step explanation:
The relative minor of C major is A minor. The concept of relative minor and major keys is found in music theory; it is defined as a minor key which has the same key signature as a major key. To find the relative minor of any major key, you count down three semitones (or half steps) from the major key's tonic (the first note of the scale). For example, starting on C (the tonic of C major), you would move down to B, then B-flat, and finally to A, which gives us the key of A minor.
A minor shares the same key signature as C major, which has no sharps or flats, making them relative keys. This relationship is essential for music composition and analysis, as it allows for smooth modulations and provides a tool to enrich the musical narrative.