This is the 658th most frequent Japanese word.
週間
"Week" or "weeks" (duration).
In this sentence, "週間" refers to the total duration of six weeks during which an activity occurred, quantifying a specific period.
私は毎週一回のピアノのレッスンを六週間受けました。
I took weekly piano lessons for six weeks.
In this example, "週間" denotes the length of the stay in weeks during a vacation.
休暇のために三週間イタリアに滞在しました。
I stayed in Italy for three weeks on vacation.
Here, "週間" is used to specify a planned duration of two weeks for completing the project.