"Capacity for logic, perceiving and retaining information as knowledge."
Intelligence is one of the 10 traits that can be developed during the game. It directly affects any activity that requires logic to complete such as doing math problems and participating in the science fair.
"Solving puzzles and doing activities related to science and technology with high intelligence is fun and easy and yields positive effects."
"Doing tasks that require mental effort with low intelligence would most likely confuse you and make you unhappy."