saturday is the seventh day of the week. Its role in English language is to refer to this day in time. The rules associated with its use are that it is always capitalized and that it follows other names or words when used in a date format.
1. Saturday is my favorite day of the week.
2. I'm having a party this Saturday.
3. Saturday night is just the best!
saturday can be used as an adjective when referring to something that happened or will happen on Saturday, e.g. a Saturday night special. Additionally, Saturday is commonly abbreviated as 'Sat' when used in a date format.