B4 is a type of chemical compound known as a boron compound, specifically a boron tetrafluoride complex. It is often used in various industrial applications, including as a catalyst in chemical reactions and in the production of certain materials. B4 can also refer to a specific grade of boron used in semiconductor manufacturing. In the context of music, B4 is a note in the musical scale, specifically the B note in the fourth octave. This note is commonly used in various musical compositions and is significant in both classical and contemporary music. Musicians often refer to B4 when discussing pitch and harmony in their works.