A cocoon star is a star that is a strong source of infrared but is invisible at optical wavelengths because it is shrouded by a dense individual cloud of gas and dust. Some such stars are less than a million years old and are hidden by material left over from their formation. Others are red giants or supergiants, in an advanced stage of evolution, that have ejected the material that makes their cocoon. Some of these aging cocoon stars are OH-IR sources.