Cocci are a type of bacteria characterized by their spherical shape. They can exist as single cells or form clusters, chains, or pairs. Cocci are classified into different groups based on their arrangement, such as diplococci (pairs), streptococci (chains), and staphylococci (clusters). These bacteria can be found in various environments, including soil, water, and the human body. Some cocci are harmless and even beneficial, while others can cause infections and diseases. For example, Streptococcus pneumoniae is a type of cocci that can lead to pneumonia, while Staphylococcus aureus can cause skin infections. Understanding cocci is important in fields like microbiology and medicine.