Halloweek occurs once per year. It is a set 5-7 days where you will see girls galavanting about in themed costumes, with equally enthused guys running around.

It gives everyone a perfect excuse to get trashed and go to a theme party on a tuesday.
Meant to be taken advantage of.
Early morning lectures are optional during this week.

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A week on which October 31 usually falls within one year. It starts with costume craze and ends with tons of candy on sale. Some also consider smoking halloweed.