Staphylococcus bacteria. Coccus (plural cocci) is a term used to describe 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.Coccus is an English loanword of a Neolatin noun, which in turn stems from the Greek masculine noun kokkos (κόκκος) meaning berry.t is one of the three distinct bacterial shapes, the other two being bacillus (rod-shaped) and spiral-shaped cells. Coccus is an English loanword of a Neolatin noun, which in turn stems from the Greek masculine noun kokkos (κόκκος) meaning berry.