The moment of inertia is a measure of an object's resistance to changes in its rotation. It depends on the mass of the object and how that mass is distributed relative to the axis of rotation. A larger moment of inertia means the object is harder to spin, while a smaller moment of inertia allows for easier rotation. 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 can be calculated using various formulas depending on the shape of the object, such as cylinders, spheres, or rods.