A Fermat pseudoprime is a composite number that passes the Fermat primality test for a given base, making it appear prime. This occurs when the number satisfies Fermat's little theorem, which states that if p is a prime and a is an integer not divisible by p , then a^(p-1) \equiv 1 \mod p . However, unlike true primes, Fermat pseudoprimes can be misleading. They can lead to incorrect conclusions about a number's primality, especially when using the Fermat test with certain bases. Notably, Carmichael numbers are a specific type of Fermat pseudoprime that pass the test for all bases.