Fluid intelligence refers to the ability to solve new and abstract problems, think logically, and identify patterns without relying on prior knowledge. It involves cognitive processes like reasoning and problem-solving. Crystallized intelligence, on the other hand, involves the use of learned knowledge, experience, and skills. It includes vocabulary, general knowledge, and expertise acquired over time. Both types of intelligence are important, and IQ tests typically assess a combination of both to provide a comprehensive measure of cognitive abilities.