Aptitude test: Aptitude refers to a person's capacity to learn, and an aptitude test is designed to predict how well you will perform at something in the future, like in college, or a particular job. An achievement test, on the other hand, is designed to measure how well you did, such as how well you did in high school (the SAT for example).
Cognitive ability test: This type of test is designed to measure a person's intelligence and general mental ability. Modern psychology is moving away from terms like “IQ test” or “intelligence test” and using the more general term cognitive ability test instead.
Crystallized intelligence: There are two main types of intelligence, fluid and crystallized intelligence. Crystallized is the sum of all your learned knowledge that you've developed over time. The capital of the United States, your phone number, etc., are all crystallized intelligence.
Fluid intelligence: Fluid intelligence is the opposite of crystallized intelligence. It's “hard-wired” into your brain and cannot be changed. Solving a visuospatial puzzle is something that would require fluid intelligence. Fluid is considered genetic, while crystallized is learned.
Intelligence: In response to the highly controversial book, The Bell Curve, fifty-two of the leading psychologists of the time wrote an open letter to the scientific community—later published in The Wall Street Journal in 1994—which I feel gives the best, most thorough definition of intelligence: Intelligence is a very general mental capability that, among other things, involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly, and learn from experience. It is not merely book learning, a narrow academic skill, or test-taking smarts. Rather, it reflects a broader and deeper capability for comprehending our surroundings—“catching on,” “making sense” of things, or “figuring out” what to do.
Intelligence quotient (IQ): This is a mathematical formula that is defined as the ratio of mental age (MA) to chronological age (CA) multiplied by 100 (thus IQ = MA/CA × 100). For example, if a 15-year-old answers the questions like an average 15-year-old would, the person would have an IQ of 100 (15/15 × 100 = 100).