The moment of inertia of an I-beam, denoted as I, is a geometrical property that measures its resistance to bending. It represents the second moment of area about the centroidal axis perpendicular to the plane of bending. A higher moment of inertia indicates a beam’s ability to withstand bending forces and deformations. It plays a crucial role in beam design, as it determines the beam’s deflection and bending stress under applied loads.