It is a contraction of the phrase ‘All Hallows Eve” the night before all hallows day IE All Saints Day. It is a celebration in the Church of all the faithful departed, particularly those who where martyred for the faith.
It is thought to be a co-opting of the Celtic Samhain, but other scholars claim that Halloween sprung up on its’ own.
Christmas was once the celebration of Saturnalia. It was a very big Roman holiday. The agricultural deity Saturn was honored. The holiday was celebrated with a sacrifice at the Temple of Saturn, in the Roman Forum, and a public banquet, followed by private gift-giving, continual partying, and a carnival atmosphere. It was one of the few Empire Wide celebrations.
Regardless. It is fun. It should be celebrated for the fun of it. Life is too short to be a stick in the mud.
There’s more to All Hallows Eve than that. Treats were left on doorsteps to keep ghouls and goblins sated. That where “trick or treat” comes from. Covens have celebrated it for a very long time. As I said, they do not celebrate Christ’s birth or death.