- Apitude: A capacity for learning certain abilities
- Chronological Age: A person's age in years
- Cretinism: Stunted growth and mental retardation caused by an insufficient supply of thyroid hormone
- Culture-Fair Test: A test designed to minimize the importance of skills and knowledge that may be more common in some cultures than in others
- Down Syndrome: A genetic disorder caused by the presence of an extra chromosome; results in mental retardation
- Early Childhood Education Program: Programs that provide stimulating intellectual experiences, typically for disadvantaged preschoolers
- Eugenics: Selective breeding for desirable characteristics
- Experiential Intelligence: Specialized knowledge and skills acquired through learning and experience
- Fragile-X Syndrome: A genetic form of mental retardation caused by a defect in the X chromosome
- Fraternal Twins: Twins conceived from two separate eggs
- G-Factor: A core of general intellectual ability that is assumed to explain the high correlations among various measures of intelligence
- General Intelligence Test: A test that measures a wide variety of mental abilities
- Giftedness: Either the possession of a high IQ or special talents or apitudes
- Group Intelligence Test: Any intelligence test that can be administered to a group of people with minimal supervision
- Hydrocephaly: A buildup of cerebrospinal fluid within brain cavities
- identical Twins: Twins who develop from a single egg and have identical genes
- Individual Intelligence Test: A test of intelligence designed to be given to a single individual by a trained specialist
- Inspection Time: The amount of time a person must look at a stimulus to make a correct judgment about it
- Intelligence: An overall capacity to think rationally, act purposefully, and deal effectively with the environment
- Intelligence Quotient (IQ): An index of intelligence defined as mental age divided by chronological age and multiplied by 100
- Mental Age: The average mental ability displayed by people of a given age
- Mental Retardation: The presence of a developmental disability, and IQ score below 70, or a significant impairment of adaptive behavior
- Metacognitive Skills: An ability to manage one's own thinking and problem-solving efforts
- Microcephaly: A disorder in which the head and brain are abnormally small
- Multiple Aptitude Test: A test that measures two or more aptitudes
- Multiple Intelligences: Howard Gardener's theory that there are several specialized types of intellectual ability
- Neural Intelligence: The innate speed and efficiency of a person's brain and nervous system
- Norm: An average score for a designated group of people
- Normal Curve: A bell-shaped curve characterized by a large number of scores in a middle area, tapering to very few extremely high and low scores
- Objective Test: A test that gives the same score when different people correct it
- Operational Definition: The operations used to measure a concept
- Performance Intelligence: Intelligence measured by solving puzzles, assembling objects, completing pictures, and other nonverbal skills
- Phenylketonuria: A genetic disease that allows phenylpyruvic acid to accumulate in the body
- Reflective Intelligence: An ability to become aware of one's own thinking habits
- Reliability: The ability of a test to yield the same score, or nearly the same score, each time it's given to the same person
- Special Aptitude Test: A test used to predict a person's likelihood of succeeding in a particular area of work or skill
- Speed of processing: The speed with which a person can mentally process information
- Terminal Decline: An abrupt decline in measured intelligence about five years before death
- Test Standardization: Establishing standards for administering a test and interpreting scores
- Validity: The ability of a test to measure what it purports to measure
- Verbal Intelligence: Intelligence measured by answering questions involving vocabulary, general information, arithmetic, and other language-or symbol-oriented tasks