Davourak

I also thought that maybe it means how many times the gold has been milled to make it into gold leaf to use for coating the coin? Or maybe 100 layers of gold leaf? Some are listed as 100 mills, some as 500 mills.

But what does the "mills" refer to? Sounds like millimetres but obviously not. Maybe micrometres?

Hello, I am new to coin collecting. I have seen some coins advertised along the lines of "24k gold 100 mills". What does the 100 mills refer to? I tried searching online and found nothing (I guess the word mills is too generic).