What is Saturday ?
Saturday is (noun) the sixth day of the week, the day between Friday and Sunday We arranged to meet up on Satur- day. He works in a shop, so Saturday is a normal working day for him. We go shop- ping in London most Saturdays. Saturday is the Jewish day of rest. Today is Satur- day, November 15th. The 15th is a Satur- day, so the 16th must be a Sunday.
source: Easier English, Student Dictionary Upper Intermediate Level