What is polychromatic light?

Hint: Seven distinct wavelengths corresponding to a particular combine to form white light. Therefore, we can say that white light is made of seven distinct colours which fall in the visible region of the electromagnetic spectrum. Depending on the number of colours, light can be polychromatic or monochromatic.

Complete answer:
Light is made up of different wavelengths. Each wavelength corresponds to a particular colour. When the light is divided into its seven component colours, it is known as a spectrum.
Light can be made by combining all the seven component wavelengths or by using one or more than one component wavelengths.
Light which consists of more than one of the visible wavelengths is called polychromatic light or the light which is made of more than one colour is called polychromatic.
Wavelengths bend around obstacles whose sizes are comparable to their wavelengths therefore, in diffraction, using a polychromatic light will not give us distinct bright and dark fringes. Also, interference patterns cannot be observed using polychromatic light as the interference patterns overlap each other.
Therefore, polychromatic light is made up of more than one wavelength.

Note:
All the wavelengths that make up white light fall in the visible region of electromagnetic radiation. Interference is a phenomenon in which light from coherent sources superimpose to form a distinct pattern on a screen. Diffraction is a phenomenon in which light bends around obstacles to spread in a region of geometrical shadow. The seven colours in the spectrum are violet, indigo, blue, green, yellow, orange, red.