What are iridescent clouds?

Arabia Weather - Iridescent clouds or the phenomenon of cloud iridescence is a colorful optical phenomenon that appears on clouds, and usually appears next to the sun or moon, and resembles the colors that appear on soap bubbles or oil drops on the surface of water.

This phenomenon has been observed in cumulus clouds, cirrocumulus, lenticular clouds, and icy clouds. They sometimes appear in clusters parallel to the cloud edge, and have also been seen on rare polar stratospheric clouds, also known as nacreous clouds.