Bacteria belong to the domain Bacteria, which is one of the three major domains of life. The other two domains are Archaea and Eukarya. Bacteria are prokaryotic organisms, meaning they lack a nucleus and other membrane-bound organelles, which distinguishes them from eukaryotic cells that make up plants, animals, and fungi.
This classification is based on genetic similarities and differences. The domain Bacteria encompasses a vast array of single-celled organisms that can be found in nearly every environment on Earth, from soil and water to extreme conditions like hot springs and deep-sea vents. Bacteria play essential roles in various ecological processes, including decomposition, nitrogen fixation, and as part of the human microbiome.