Halloween is a holiday celebrated both in the real world and the SpongeBob SquarePants universe, where many of the characters dress in costumes and throw Halloween-themed parties.
Role in series
SpongeBob attempts to make himself look scary and then dresses up as a ghost himself, which causes everyone else to become frightened.
A Halloween party is then thrown at the Krusty Krab.
"The Legend of Boo-Kini Bottom"
The Flying Dutchman wants to make sure SpongeBob and his friends are scared on Halloween. He teaches SpongeBob that scary equals scary instead of funny.
- Halloween on Wikipedia