Humans have thought about the nature of intelligence for millennia. This picture is from a work by Robert Fludd published between 1617 and 1621.

Intelligence refers to certain mental powers. There is no general agreement on which mental powers are intelligent or part of intelligence. The idea comes from a Latin word: intelligo meaning to choose between different options. A part of intelligence allows people to solve problems. These problems may be easy to solve. They may also be difficult to solve, and involve abstract thought. For some, intelligence is a property, or characteristic of the mind. For others, it is simply the working of the brain, especially the cerebral cortex.