A Yilong is the longest base unit in the Chinese System of Units. If something is Yilong it is almost unreallisticly large. Countries have adopted this definition by the great flood of Chinese who decide to study elsewhere in the world, specializing in Mathematics, Economics and or Physics.
Yilong is also used in a proverbs.
When you hear somebody say: "How long is a Chinese?", you'll notice the answer is often "Yilong".