An S0 galaxy, also known as a lenticular galaxy, is a type of galaxy that has characteristics of both spiral and elliptical galaxies. It typically features a central bulge and a disk but lacks the prominent spiral arms found in spiral galaxies. S0 galaxies often contain older stars and less interstellar gas and dust, making them appear more like elliptical galaxies. These galaxies are often found in galaxy clusters and can serve as a transitional form between the two main types of galaxies. Examples of S0 galaxies include NGC 5866 and M105, which help astronomers study galaxy evolution and formation.