The name Halloween means the evening before all Hallows or all Saints Day.

万圣节前夕意为众神日或众圣日的前夕。

youdao

At 9.30 on the morning of November 1st 1755, All Saints Day, an earthquake struck Lisbon while most of the population was at church.

1755年11月1日9：30，万圣节，当大多数人都聚集在教堂的时候，一场地震袭击了里斯本。

youdao

Pope Gregory III designated November 1st as All Saints' Day, a time to honor saints and martyrs.

教皇格里高利三世将11月1日定为万圣节，以此纪念圣人和殉道者。

youdao

It originally fell around August, but the Christian conquistadors, hoping to assimilate the heathen holiday through their favoured tactic of cultural mestizaje (mixing), moved it to the day after All Saints' Day.

BBC: Mexico's Day of the Dead

Held on All Saints' Day (1 November) and All Souls' Day (2 November) according to the Catholic calendar, this Aztec-influenced festival commemorates the memory of deceased family, friends, and ancestors.

BBC: Get spooked: Five sensational Halloween destinations

Both All Hallows' Eve -- known today as Halloween -- and All Saints' Day, which follows on November 1, were designated as days to pray for dead souls that had not passed out of purgatory, in the belief that the prayers of the living will help.

CNN: Happy Halloween