Meningococcus: A type of bacteria now formally known as Neisseria meningitidis, which is responsible for a number of meningococcal diseases including epidemic bacterial meningitis, an inflammation of the coverings of the brain and spinal cord.
In technical terms, the meningococcus (Neisseria meningitidis) is a gram-negative nonmotile pyogenic coccus. The staining characteristics of bacteria provide an important classification system for the identification of bacteria. Bacteria are considered to be gram-negative if they have a red color by Gram's method of staining. (This is a primary characteristic of bacteria that have a cell wall composed of a thin layer of peptidoglycan covered by an outer membrane of lipoprotein and lipopolysaccharide containing endotoxin.) The term "nonmotile" means they do not move on their own. "Pyogenic" means they cause pus to form. And a "coccus" is a bacterium with a rounded or spherical shape, as opposed to one that is rod-shaped.