A K3 surface is a special type of complex algebraic surface that has specific geometric properties. These surfaces are characterized by having a trivial canonical bundle, which means they have no "twisting" in their structure. K3 surfaces are important in various areas of mathematics, including algebraic geometry and string theory. K3 surfaces can be thought of as higher-dimensional analogs of Riemann surfaces. They are often studied for their rich symmetry properties and connections to mirror symmetry and moduli spaces. K3 surfaces can also be used to construct Calabi-Yau manifolds, which are significant in theoretical physics, particularly in string theory.