Intelligence is the capacity to understand the world, think rationally, and use resources effectively when faced with challenges.
Definition 2.
Intelligence refers to
1. The product resulting from the collection, processing, integration, evaluation, analysis, and interpretation of available information concerning foreign nations, hostile or potentially hostile forces or elements, or areas of actual or potential operations.
2. The activities that result in the product.
3. The organizations engaged in such activities.
Although psychologists have been discussing this concept since the 1870s there is no general agreement on what intelligence is. Most psychologists would probably agree that heredity sets the limits of a person's intelligence and most would agree that the ability to learn in one form or another (handling abstract ideas, adapting to new situations, perceiving complex relationships) is a sign of high intelligence-which doesn't get us very far but has never prevented psychologists from designing new intelligence tests. Intelligence is a good example of a phenotype.