what is bacterial
bacteria. pl n, sing-rium (-rÉªÉm). 1. (Microbiology) a very large group of microorganisms comprising one of the three domains of living organisms.They are prokaryotic, unicellular, and either free-living in soil or water or parasites of plants or animals.See also prokaryote.oun. 1. bacteria - (microbiology) single-celled or noncellular spherical or spiral or rod-shaped organisms lacking chlorophyll that reproduce by fission; important as pathogens and for biochemical properties; taxonomy is difficult; often considered to be plants. bacterium.