Longman Dictionary of Contemporary English - saturday

~ n the day between Friday and Sunday. In Britain, Saturday is considered the sixth day of the week, and in the US it is considered the seventh day of the week  (on Saturday)  (We went for a picnic on Saturday. | Deats always goes home on Saturdays. | last/next Saturday)  (I saw Sally last Saturday at the Mall. | on a Saturday)  (My birthday is on a Saturday this year.)