Halloween is an annual holiday/party day that takes place in October 31st. Half-A-Ween/Half-O-Ween is defined as the day that is between, in the middle, of the previous and upcoming Halloween day. The actual day is May 1st. However, since it is not an official holiday, people celebrate it by dressing up just like Halloween roughly in May or June hence the name Half-A-Ween/Half-O-Ween.
However, its just an excuse for people to celebrate and dress up. It really has nothing to do with
Paganism,
Christianity or any cultural references. Its a holiday created by young adults that was born in the 80s and needed something to reminiscence their childhood.