Type IIb refers to a classification of certain types of supernovae, which are explosive events marking the death of massive stars. These supernovae are characterized by the presence of hydrogen in their spectra, but they also show signs of helium and other elements. This indicates that the star has undergone significant changes before its explosion. In the context of stellar evolution, Type IIb supernovae occur when a massive star loses its outer hydrogen layer, often due to strong stellar winds or interactions with a companion star. This results in a core collapse that leads to the supernova explosion, leaving behind a neutron star or black hole.