Psychologists characterise intelligence differently from the common sensical notion. An intelligent person typically shows attributes like mental alertness, ready wit, quickness in learning, and the ability to understand relationships. The Oxford Dictionary explains it as the power of perceiving, learning, understanding, and knowing.

Early theorists used these attributes to define intelligence. Alfred Binet, one of the first psychologists to work on intelligence, defined it as the ability to judge well, understand well, and reason well.

Another prominent psychologist, Wechsler, understood intelligence in terms of its functionality, specifically its value for adaptation to the environment. He defined it as the global and aggregate capacity of an individual to think rationally, act purposefully, and deal effectively with the environment.

Furthermore, people differ in their ability to understand complex ideas, adapt to environment, learn from experience, engage in various forms of reasoning, and overcome obstacles.

Psychologists have also proposed different approaches to characterise intelligence. The psychometric approach considers intelligence as an aggregate of abilities, expressing performance in a single index of cognitive abilities. In contrast, the information-processing approach describes the processes people use in intellectual reasoning and problem-solving, focusing on how an intelligent person acts.