Any of a division (Bacteria) of monerans, microorganisms which are typically one-celled, have no chlorophyll, multiply by simple division, and can be seen only with a microscope: they occur in three main forms, spherical (cocci), rod-shaped (bacilli), and spiral (spirilla): some bacteria cause diseases such as pneumonia and anthrax, and others are necessary for fermentation, nitrogen fixation, etc.
The definition of bacteria are microorganisms that are the basis of fermentation and infectious diseases.
An example of bacteria are the organisms that cause common human illnesses like strep throat.
(US) A type, species, or strain of bacterium.
Origin of bacteria
From New Latin bacteria, plural of bacterium, from Ancient Greek βακτήριον (baktērion), neuter diminutive of βακτηρία (baktēria, “rod, stick”).