A Carmichael Number is a special type of composite number that satisfies Fermat's Little Theorem for all integers that are coprime to it. This means that if you take any integer a that does not share any factors with the Carmichael number, raising a to the power of the number minus one will yield a result congruent to 1 modulo the Carmichael number. These numbers are significant in number theory because they can mislead primality tests, making them appear prime when they are not. The smallest Carmichael number is 561, and they are also known as absolute pseudoprimes.