A pseudoprime is a composite number that passes certain tests for primality, making it appear to be a prime number. Specifically, it satisfies the conditions of the Fermat primality test, which checks if a number behaves like a prime under specific mathematical conditions. However, since it is not actually prime, it can mislead those who rely solely on this test. Pseudoprimes are important in number theory and cryptography, as they help researchers understand the limitations of primality tests. The most well-known type is the Fermat pseudoprime, which is a composite number that remains undetected by the Fermat test for some bases.