Streptococcus pneumoniae (pneumococcus): A type of bacterium that comes in pairs and is shaped like a lancet (a surgical knife with a short wide two-edged blade).
Pneumococcus is the leading cause of bacterial pneumonia and otitis media (middle ear infections) and an important contributor to bacterial meningitis. Pneumococcal infections are the most common invasive bacterial infections in children in the United States, causing about 1,400 cases of meningitis, 17,000 cases of bloodstream infections, and 71,000 cases of pneumonia every year in children under 5.
Vaccines now exist for those individuals at high risk of infection with this bacterium.
The formal name of the bacterium is currently Streptococcus pneumoniae. (The "strepto-" means twisted and "-coccus" comes from the Greek kokkos meaning berry.) Because of its coming in pairs, it has also been called Diplococcus pneumoniae. "Pneumoniae" refers to its propensity to settle in the lungs and cause pneumonia.