 Semilattices, left-zero bands, right-zero bands, rectangular bands, normal bands, left-regular bands, right-regular bands and regular bands, specific subclasses of bands that lie near the bottom of this lattice, are of particular interest and are briefly described below.A class of bands forms a variety if it is closed under formation of subsemigroups, homomorphic images and direct product.Each variety of bands can be defined by a single defining identity.