NaN% is the percentage you get when you try to turn the fraction sitemap.xml / undefined into a percent.
Since the denominator “undefined” has no numeric value, the whole expression cannot be calculated. That’s why the result shows up as “NaN”, which stands for “Not a Number”. It tells you that the math doesn’t make sense in the usual way.
In everyday work, you’ll rarely see a real fraction like this. If a tool or script tries to divide by something that isn’t defined, it will often return NaN% as a placeholder to warn you that something went wrong.
So whenever you spot NaN%, think of it as a signal to check the numbers you’re using, because the calculation can’t be completed as written.
