An H II region is a large cloud of gas and dust in space that is primarily composed of ionized hydrogen. These regions are often found around young, hot stars, which emit ultraviolet light that ionizes the surrounding hydrogen gas. This process creates a glowing nebula, making H II regions visible in the night sky. H II regions are important for understanding star formation and the evolution of galaxies. They often serve as stellar nurseries, where new stars are born from the surrounding gas and dust. Examples of well-known H II regions include the Orion Nebula and the Lagoon Nebula.