How are relative keys different from parallel keys?

In music theory, the distinction between relative and parallel keys lies in their relationship to the key signature and the tonic note.12

• Relative Keys: A major key and a minor key are considered relative if they share the exact same key signature. For example, C major and A minor both have no sharps or flats. On the circle of fifths, relative major and minor keys occupy the same position, with the minor key typically represented on an inner layer.12
• Parallel Keys: Parallel keys share the same tonic note but utilize different scales and key signatures. For instance, C major and C minor are parallel keys; while they both center on the note C, they differ in their internal scale structure and the number of sharps or flats in their signatures.1

These relationships are fundamental to tonality, as they help composers organize harmony and navigate modulation between different tonal centers.13