Definition:
Cognitive is a psychological process involved in acquisition and understanding of knowledge, formation of beliefs and attitudes which helps in decision making, problem solving. They are distinct from emotional and volitional processes involved in wanting and intending. Cognitive capacity is measured generally with intelligence quotient (IQ)
The ability to quickly and effectively perform complex and challenging tasks makes cognitive power a key determinant of success.
Further Reading:
https://en.wikipedia.org/wiki/Cognition