Taxonomy

Living things are called organisms. All organisms fall under one of the three domains: Bacteria, Archaea, or Eukarya. 

Prokaryotic, unicellular organisms are part of Bacteria or Archaea. Bacteria includes all the bacteria. Archaea includes extremophiles (organisms that live in extreme environments). Archaea is not associated with diseases.

Eukaryotic organisms are part of Eukarya, which has 4 kingdoms: Animalia, Plantae, Fungi, and Protista.
Animals, Plants, and Fungi are all multicellular. Protists can be unicellular or multicellular.

Every organism is classified according to the standard taxonomy chart, which starts at domain and ends at species. The scientific name for an organism is its genus and species.