By a monochromatic wave, we mean ?

A monochromatic wave refers to a wave that consists of a single frequency or wavelength. It is a pure wave of a single color or tone, without any mixture or variation in frequency. In other words, it is a wave that oscillates at a single, well-defined frequency.

Monochromatic waves are often used as a simplifying assumption in physics and mathematics to analyze wave behavior. They are commonly encountered in fields such as optics, where lasers produce highly monochromatic light waves. In these cases, the waves have a very narrow range of frequencies or wavelengths, which allows for precise control and manipulation of the wave properties.