Be star is a B-type star with prominent emission lines in its spectrum. Other observational characteristics include optical linear polarization and often infrared radiation that is much stronger than in ordinary B-class stars.

All the observational characteristics are explained with a strong, asymmetric stellar wind from the star. Often the wind forms a circumstellar disk. The strong emission lines and infrared radiation come from the wind, and scattering of the stellar light from the disk produces the polarization.