The word 'intelligence' originates from the Latin verb 'intelligere' and refers to the ability to comprehend or perceive, with various definitions and theories proposed by psychologists like Terman, Wechsler, and Gardner. Intelligence is characterized by the abilities to learn from experience, adapt to new situations, understand abstract concepts, and manipulate one's environment. Overall, there is a general consensus among psychologists that adaptation to the environment is key to understanding intelligence.