Staphylococcus is a genus of Gram-positive bacteria that are found in various environments, including the human body. They are spherical or ovoid in shape and can be found in clusters. Staphylococcus is a common cause of skin infections, food poisoning, and other illnesses. The term 'staph' is derived from the Greek word for 'bunch of grapes, ' which describes the clustered arrangement of the bacteria.