Eukaryote: An organism that consists of one or more cells each of which has a nucleus and other well-developed intracellular compartments.Eukaryotes include all organisms except bacteria, viruses, and certain (blue-green) algae which, by contrast, are prokaryotes.See: Prokaryote.t is this nucleus that gives the eukaryote its name. Eukaryote means true nucleus. Eukaryotic organisms also have other specialized structures, called organelles, which are small structures within cells that perform dedicated functions. As the name implies, you can think of organelles as small organs.