The term "irreducible" refers to something that cannot be simplified or broken down into smaller parts. In mathematics, an irreducible fraction is one where the numerator and denominator have no common factors other than 1, meaning it cannot be reduced further. For example, the fraction 3/4 is irreducible, while 6/8 can be simplified to 3/4. In science, "irreducible" can describe certain complex systems or structures that cannot be simplified without losing their essential properties. For instance, an irreducible representation in group theory is a way of expressing a group that cannot be decomposed into simpler representations.