Intelligence has been defined in many different ways, including the abilities, but not limited to, abstract thought, understanding, self-awareness, communication, reasoning, learning, having emotional knowledge, retaining, planning, and problem solving.
Intelligence is most widely studied in humans, but has also been observed in animals and plants. Artificial intelligence is the intelligence of machines or the simulation of intelligence in machines.
As a reference for the above passage, and for more information see Intelligence.
This tag is for questions on the levels of the above-listed abilities, the roles of these levels in education, testing such levels, and deficiencies in these areas.