A "Perfect Interval" in music theory refers to a specific distance between two notes that is perceived as consonant and stable. The most common perfect intervals are the perfect fourth and perfect fifth, which are essential in forming chords and harmonies. These intervals are called "perfect" because they have a pleasing sound and are foundational in Western music. In terms of frequency ratios, a perfect fifth has a ratio of 3:2, while a perfect fourth has a ratio of 4:3. These ratios contribute to the harmonious quality of the intervals, making them vital in the construction of scales and melodies. Understanding perfect intervals is crucial for musicians and composers when creating music.