A diplococcus (plural diplococci) is a round bacterium (a coccus) that typically occurs in the form of two joined cells. Examples are gram-negative Neisseria sp., and gram-positive Streptococcus sp. and Staphylococcus sp..
Its name comes from diplo, meaning double, and coccus, meaning berry.
In former times, a bacterial genus Diplococcus was recognized, but it is not used anymore.