A semitone is the smallest musical interval commonly used in Western music. It represents the distance between two adjacent keys on a piano keyboard, whether they are white or black. For example, moving from C to C# or from E to F covers one semitone. In music theory, semitones are essential for constructing scales and chords. A whole tone consists of two semitones, which means that moving from C to D involves two semitones: C to C# and C# to D. Understanding semitones helps musicians create melodies and harmonies effectively.