Summary
A genius is an individual with an exceptional capacity for knowledge and intelligence. Geniuses can appear in a variety of forms and with a variety of specialties, and their exceptional intelligence is not necessarily universal, potentially only applying to certain subjects and fields that they excel in. These can be any number of things, such as scientific fields, military tactics, martial arts, and/or investigation. There are many levels of genius, as well, detailed on the intelligence page; a regular genius, on the level of those that exist in the real world, is generally limited to a few areas of expertise, while fictional individuals of greater intellects may be masters of many, if not all fields of science and even strategy as well.
Examples
Geniuses: Nermal, Julia RockLiger and Joly Biggs (Kitty Pride), Rockstar (Insiders)
Extraordinary Geniuses: Drake Biggs (Kitty Pride), Carla (2046: Prime)
Supergeniuses: Doctor Doom and Kang the Conqueror (Avengers Alliance)