The weekend before Halloween (starting on Thursday and ending on Sunday or whatever day Halloween falls on). It do not matter what day of the week Halloween is because parties happen all weekend long. Halloweekends are usually at colleges where they party hard. Many people have multiple costumes for each night of Halloweekend.
James: Man, my professor scheduled an exam the Monday after Halloweekend.
Ryan: That sucks! I'll be partying hard all Halloweekend!