40 that each year the young women of Israel go out for four days to commemorate the daughter of Jephthah the Gileadite.

Read Judges 11:40 Using Other Translations

That the daughters of Israel went yearly to lament the daughter of Jephthah the Gileadite four days in a year.
that the daughters of Israel went year by year to lament the daughter of Jephthah the Gileadite four days in the year.
for young Israelite women to go away for four days each year to lament the fate of Jephthah’s daughter.