Eukaryota is a group of living organisms having a nucleus and mitochondria. It is one of the three main groups of living beings (the other two being bacteria and archea). All plants, animals and protozoans are eukaryotic. The name comes from greek and signifies the presence of a true (eu-) nucleus (karyon).

Eucarya is one of the Three Domains. This Domain made of eucaryotes (also spelled eukaryotes) which possess membrane bound organelles and a nucleus. Eucarya are believed to be more closely related to Archaea than Eubacteria based on similarities in biosynthetic pathways and other evidence, like the presence of introns in some Archaea and eukaryotes.