What is the definition or description of: bacteria?

Single cell organism: Bacteria are single cell organisms which are neither plant or animal. Most do not have separate nucleus which differentiate them from other single cell organsisms like an amoeba bacteria are very important to life on the planet. A very few species are harmful, but the most are benign and in fact many are important.

Single celled life: Are omnipresent single celled organisms which are the both the simplest form of life and the original form of life on earth. The are also called 'prokaryotic' organisms.

Microscopic organism: A large group of single-celled microscopic organisms found almost anywhere on earth.Millions of yrs older than humans, their sizes and shapes are diverse, and can grow in extreme environments.Though some can cause diseases, these bacteria and many others also help in important bodily activities (eg. Digestion), industry (like alcohol production), and food production (eg. Turning milk to cheese).