A "Perfect Fourth" is a musical interval that spans four diatonic scale degrees. In Western music, it is defined as the distance between the first note (the root) and the fourth note of a major or minor scale. For example, in the C major scale, the notes are C, D, E, F, and the interval from C to F is a perfect fourth. This interval is considered consonant, meaning it sounds stable and pleasant when played together. Perfect fourths are commonly used in various musical contexts, including harmony, chord progressions, and melody construction, making them fundamental in both classical and contemporary music.