Halloween (All Hallows Eve) is the eve (day before) All Souls Day, which is a Catholic holiday.
So when people who call themselves Christian say that Halloween is a satanic holiday, they don't know what they are talking about.
I could get way further into this, but I'm gonna restrain myself before I spend way too much time typing just for a bunch of ignorant people to either tell me that Catholics "aren't Christian" or say they ain't readin' allat.