An Augmented Fourth is a musical interval that spans four diatonic scale degrees and is one semitone larger than a perfect fourth. For example, in the key of C major, the interval from C to F# is an augmented fourth. This interval is often used to create tension in music, leading to a resolution in harmony. In Western music theory, the augmented fourth is considered dissonant and can evoke a sense of unease. It is commonly found in various genres, including classical and jazz, and is sometimes referred to as a tritone due to its unique sound.