S. niger is an abbreviation of a species name. In binomial nomenclature, the name of a species is always the name of the genus to which the species belongs, followed by the species name (also called the species epithet). In S. niger, the genus name has been abbreviated to S. and the species has been spelled out in full. In a document that uses this abbreviation, it should always be clear from the context which genus name has been abbreviated.
The Latin species epithet niger means "black". Some of the most common uses of S. niger are: Sciurus niger, the fox squirrel, the largest species of tree squirrel Serrasalmus niger, a synonym of Serrasalmus rhombeus, the redeye piranha Sphodros niger, the black purse-web spider, a mygalomorph spider species from the eastern United States Streptanthus niger, an endangered plant species
There are many other possibilities, for example the following genus names that start with S have a species name with the epithet niger.
Vascular plants: Sicyos niger Strophanthus niger Syngonanthus niger
Beetles: Sennius niger Spermophagus niger Stenoluperus niger Syllitus niger
Spiders: Sphodros niger Stertinius niger Stiphropus niger
Other organisms: Saccharomyces niger, a yeast Saguinus niger, a monkey Scarus niger, a fish Scutovertex niger, a mite Siganus niger, a fish Stomoxys niger, an African biting fly Streptomyces niger, a bacterium Synsphyronus niger, a pseudoscorpion
See also Niger (disambiguation) Solanum nigrum Sorghum nigrum