A microbe is a microscopic organism that can exist as a single cell or a cluster of cells. They include various categories such as bacteria, viruses, fungi, and protists. Microbes play essential roles in different ecosystems, contributing to processes like nutrient cycling, decomposition, and fermentation. Some microbes are beneficial, aiding in digestion or bioremediation, while others can cause diseases. Their ubiquitous presence makes them crucial for understanding ecological interactions and the functioning of life on Earth.