Here's a comprehensive summary of the Wikipedia article on Halloween:

Halloween, celebrated annually on October 31st, marks the eve of All Hallows' Day, beginning Allhallowtide—a Christian period dedicated to remembering the dead. Its origins are debated, with some theories linking it to ancient Celtic harvest festivals like Samhain, which may have pagan roots, while others suggest it emerged independently as a Christian vigil. The holiday gained significant popularity in North America after being brought by Irish and Scottish immigrants in the 19th century, subsequently spreading globally due to American influence by the late 20th and early 21st centuries.

Today, Halloween is widely recognized for activities such as trick-or-treating, attending costume parties, and carving jack-o'-lanterns from pumpkins, often embracing themes of horror and the supernatural. While largely a secular celebration, some Christians continue traditional observances like attending church services and remembering the departed, historically abstaining from meat. The name "Halloween" itself is of Christian origin, derived from "All Hallows' Eve," meaning 'Saints' evening'.