Emission-line stars are a type of star that emits light at specific wavelengths, resulting in bright lines in their spectrum. These lines are produced by the presence of ionized gas surrounding the star, which absorbs energy and re-emits it at particular frequencies. This phenomenon is often observed in young, hot stars, especially those in the O and B spectral classes. These stars are typically found in regions of active star formation, such as nebulae. The intense radiation from the star ionizes the surrounding gas, creating a glowing effect. Emission-line stars are important for studying stellar evolution and the dynamics of interstellar matter.