This is the 5183rd most frequent Japanese word.
金曜
Friday.
The word "金曜日" (Friday) is used here to specify a particular day of the week when an event occurs or a condition holds true.
金曜日はライブラリーが休む日です。
Friday is the day the library is closed.
The word "金曜日" (Friday) in this sentence shows the temporal setting for the planned action of going to watch a movie.
金曜日に友達と映画を見に行きます。
I will go to watch a movie with my friend on Friday.
Here, "金曜日" (Friday) is used to describe which day's lessons are being referred to, indicating the noun's role as a modifier.