The moment of inertia is a measure of an object's resistance to changes in its rotation. It depends on both the mass of the object and how that mass is distributed relative to the axis of rotation. The greater the distance of the mass from the axis, the higher the moment of inertia, making it harder to spin. In physics, the moment of inertia is crucial for understanding rotational dynamics, similar to how mass is important for linear motion. It is often represented by the symbol I and is calculated using various formulas depending on the shape of the object, such as cylinders, spheres, or rods.