The classification, nomenclature, and identification of bacteria; sometimes used as a term to indicate the theory of classification. The bacteria are members of the kingdom Prokaryotae, which is defined in terms of the unique structural and biochemical properties of their cells; more specifically, the organization of the deoxyribonucleic acid (DNA) in the nucleus, the lack of a nuclear membrane, the lack of independent membrane-bounded cytoplasmic organelles, the lack of endocytosis and exocytosis, and the chemical nature of some components of plasma membrane and cell walls.