1.
the 5th of the month
Used to refer to the fifth day of a calendar month.
五月五日はこどもの日だ。
May 5th is Children's Day.
来月の五日に会議がある。
There's a meeting on the 5th of next month.
毎月五日には給料が振り込まれる。
My salary is deposited on the 5th of every month.
2.
five days (duration)
A span of five days, often in the form 五日間.
五日間出張に行く。
I'm going on a five-day business trip.
あれから五日経った。
Five days have passed since then.
連休は今年も五日間続く予定だ。
This year too the consecutive holidays are scheduled to last five days.
五日 uses the native Japanese counting series for days 1–10 of the month: 一日, 二日, 三日, 四日, 五日, 六日, 七日, 八日, 九日, 十日. The same forms also count durations in days (except 一日 for 'one day' as a duration).
DISAMBIGUATION:
Do not confuse with いつか (someday, sometime), which is written either in kana only or with kanji 何時か. The two are unrelated despite the identical reading.
COMMON COLLOCATIONS:
- 五月五日: May 5th (Children's Day)
- 毎月五日: the 5th of every month
- 五日間: five-day period