Halloween (also spelled Hallowe'en) is an annual holiday celebrated on October 31. The day’s often associated with colors black and orange, and is strongly associated with symbols like jack-o'-lantern. Halloween activities include trick-or-treating, wearing costumes and attending costume parties, ghost tours, bonfires, visiting haunted attractions, pranks, telling scary stories, and watching horror films. Since Halloween is most popular in the U.S., Google focuses on search queries to track fastest-rising searches related to [costume] in U.S. in 2009. Here’s the char of top US queries:

More info: Google blog