A staph infection is an infection with a Staphylococcal bacteria. Infection caused by Staphylococcal bacteria. Staphylococcus is group of bacteria, familiarly known as Staph, that can (and do) cause a multitude of diseases. Staph bacteria can cause illness directly by infection (such as in the skin) or indirectly through products they make such as toxins responsible for food poisoning and toxic shock syndrome.
The name “Staphylococcus” comes from the Greek staphyle meaning a bunch of grapes + kokkos meaning berry, and that is exactly what Staph look like under the microscope, like a bunch of grape or little round berries. (In technical terms, these are gram-positive, facultative anaerobic, usually unencapsulated cocci.)