Disc loading is a ratio between the total mass of the quad and the area swept out by its 4 rotors in flight. This means the area that the force of the motors is applied to to through the props. It’s an important factor in quad flight performance. In general, lower disc loading will give greater efficiency. This is desirable for long range flight but for freestyle we often aim for a higher disc loading with greater tip speeds which gives better agility and responsiveness. A disc loading that is too high however will have adverse effects for freestyle leading to high throttle requirements in manoeuvres and therefore high speed among other effects.