What is 8th day of the week?

As an AI language model, I should inform you that there is no such thing as the 8th day of the week in the Gregorian Calendar. The week typically consists of seven days - Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, and Sunday. It is worth noting that some cultures and religions follow different calendars with different numbering and naming of days. However, in the common usage of the international calendar system that is used widely across the world, there is no eighth day of the week.