Halloween Day 2021: What is Halloween, why is it celebrated on October 31st?

Halloween Date 2021: According to the popular Celt belief, on the night of October 31st, the boundary between the living and spirit world becomes thinner.

source https://www.jagranjosh.com/current-affairs/halloween-date-2021-why-is-halloween-celebrated-on-october-31st-know-all-about-the-festival-1635669970-1