The musical note with a frequency of 440 Hz is the note A4, which is commonly referred to as "A above middle C." This frequency serves as the standard reference pitch for tuning musical instruments, especially in Western music. The use of A440 frequency as a tuning standard was widely adopted in the 20th century, and it helps ensure consistency across different instruments and performances. Musicians tune their instruments to this pitch to achieve harmonious sound during performances. The A4 tuning standard has become essential in orchestras and various music genres worldwide.