The wavelength of a sound wave refers to the physical distance between two consecutive points that are in phase with each other, such as two crests or two troughs of the wave. It is a characteristic of longitudinal waves, which are waves that propagate through a medium by compressing and expanding the particles of the medium in the same direction as the wave.
On the other hand, the wavelength of an electromagnetic (EM) wave represents the distance between two consecutive points in the wave where the electric and magnetic fields are at the same phase. Electromagnetic waves are transverse waves, meaning that the oscillations of the electric and magnetic fields are perpendicular to the direction of wave propagation. Unlike sound waves, electromagnetic waves do not require a medium to propagate and can travel through vacuum.
The key difference between the two is that sound waves require a medium (such as air, water, or a solid material) to propagate, while electromagnetic waves can propagate through vacuum as well as through various mediums. Additionally, sound waves have relatively longer wavelengths in the audible range (around 20 Hz to 20,000 Hz), whereas electromagnetic waves can have a wide range of wavelengths, spanning from very long radio waves (measured in meters or kilometers) to very short gamma rays (measured in picometers or femtometers).
In summary, the main distinctions between the wavelength of a sound wave and an electromagnetic wave are the nature of the wave (longitudinal vs. transverse), the requirement of a medium for propagation, and the range of wavelengths observed.