Frustum culling is a performance optimization technique used in computer graphics to improve rendering efficiency. It involves determining which objects in a 3D scene are within the camera's view, known as the view frustum. By only rendering objects that fall within this visible area, the system can save processing power and memory, leading to smoother performance. This technique is particularly important in real-time applications like video games and simulations, where rendering every object can be computationally expensive. By excluding objects outside the view frustum, developers can focus resources on what the player or user can actually see, enhancing the overall experience.