A coccus (plural cocci) is any bacterium that has a spherical, ovoid, or generally round shape. It is one of the three distinct bacterial shapes, the other two being bacillus (rod-shaped) and spiral-shaped cells.
Cocci is an English loanword of a modern or neo-Latin noun, which in turn stems from the Greek masculine noun kokkos (κόκκος) meaning "berry".
Cocci may occur as single cells or remain attached following cell division. Those that remain attached can be classified based on cellular arrangement:Diplococci are pairs of cocci (e.g. Streptococcus pneumoniae and Neisseria gonorrhoeae)
Streptococci are chains of cocci (e.g. Streptococcus pyogenes).
Staphylococci are irregular (grape-like) clusters of cocci (e.g. Staphylococcus aureus).
Tetrads are clusters of four cocci arranged within the same plane (e.g. Micrococcus sp.).
Sarcina is a genus of bacteria that are found in cuboidal arrangements of eight cocci.