A eukaryote (IPA: /juːˌkarɪəʊt/), also spelled eucaryote, is an organism with a complex cell or cells, in which the genetic material is organized into membrane-bound nucleus/nuclei. eukaryotes comprise animals, plants, and fungi; which are mostly multicellular, as well as various other groups that are collectively classified as protists (many of which are unicellular). In contrast, other organisms, such as bacteria, lack nuclei and other complex cell structures; such organisms are called prokaryotes. The eukaryotes share a common origin, and are often treated formally as a superkingdom, empire, or domain. The name comes from the Greek ευ, meaning good, and κάρυον, meaning nut, in reference to the cell nucleus).