NISMO is an entirely separate branch of Nissan, one which concerns itself with speed, maneuverability, and handling, over other considerations. If you want fast, you want NISMO. Formed in 1984, this branch of the Nissan family is now primarily involved in creating tune-up kits for Nissan cars, complete Nissan cars, as well as being the in house tuning and motorsports division of Nissan. NISMO currently partakes in Super GT, Blancpain GT Series, and Formula E.
In a way, NISMO can be considered to have been born in the 1960s when Nissan created Oppama Works and Omori works. These two were incorporated into a singular entity in 1984 called NISMO.