Cocci are a type of bacteria characterized by their spherical shape. They can exist as single cells or form clusters, chains, or pairs. Common examples of cocci include Staphylococcus, which often appears in clusters, and Streptococcus, which typically forms chains. These bacteria can be found in various environments, including soil, water, and the human body. Cocci can be classified based on their arrangement and staining properties. For instance, Gram-positive cocci retain a purple stain during the Gram staining process, while Gram-negative cocci do not. Some cocci are harmless, while others can cause infections, making them important in both medical and environmental contexts.