Use a custom list to sort or fill in a user-defined order. Excel provides day-of-the-week and month-of-the year built-in lists, but you can also create your own custom list. To understand custom lists, it is helpful to see how they work and how they are stored on a computer. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.