Hi there! A d66 table is an industry term that refers to a table where you roll two d6, but instead of adding them together, you use the first number as the tens and the second as the units. So if you roll a three and a one, you get 31. That's why it starts at 11 and then goes to 16, and then to 21. It's not actually 66 entries; it's just 36 entries, but the name d66 is the default used in the RPG space. Hope that helps!