If you alphabetize all the days of the week, Saturday will be the day that is listed as the third day. As we properly alphabetize the names, we will put the names in order by their first letters. If the names share the same first letter, then we use the second letter to put them in order. If the names share the first and second letters, then we use the third letter, and so on.

There are 7 days in a week. The 5 weekdays are: Monday, Tuesday, Wednesday, Thursday, and Friday. Saturday and Sunday are part of the week and form the weekend. When all the days of the week are placed in alphabetical order (the indexing method where each day is arranged in the same sequence as the letters of the alphabet (A-Z), the 7 days are: Friday (Germanic goddess Frigga associated with Venus), Monday (associated with the Moon), Saturday (associated with Saturn), Sunday (associated with the Sun), Thursday (Germanic god of thunder Thor), Tuesday (from the god Tiw, associated with Mars), and Wednesday (Germanic god Odin).

Also, to expound a little, we know that each day (Monday through Sunday) is important because it is a unit of time. It (each day) is a period of 24 hours, especially from twelve o’clock one night to twelve o’clock the next night, during which the planet earth completes one rotation on its axis.

More Info: en.wikipedia.org