Wavelength Division Multiplexing (WDM) is a technology used in fiber optic communication that allows multiple signals to be transmitted simultaneously over a single optical fiber. It achieves this by using different wavelengths, or colors, of light to carry separate data streams, effectively increasing the capacity of the fiber without needing additional cables. WDM is particularly useful for telecommunications and internet services, as it enables efficient data transmission over long distances. By combining multiple wavelengths, service providers can optimize their networks, reduce costs, and improve overall performance, making it a vital component in modern communication infrastructure.