Halloween was a human holiday celebrated on the 31st day of October. The holiday developed from several older religious festivals, and emphasized ideas and characters that were frightening to most humans.
The alien explorers Korob and Sylvia constructed a castle, took on the roles of a wizard and sorceress, and used other constructs which reminded humans such as Captain James T. Kirk and Doctor Leonard McCoy of Halloween. (TOS episode: "Catspaw")
Upon discovering a number of apparently dead Cardassian soldiers lying in a previously sealed compartment on Deep Space 9, the senior staff decided to keep the discovery a secret until a way could be found to return the Cardassians to their own people. Captain Benjamin Sisko remarked that until a diplomatically acceptable way to remove those soldiers could be found that it would be Halloween on the station. (DS9 novel: Station Rage)
In 1984, Roberta Lincoln dressed as Sally Ride for Halloween. That same year she noticed Humans dressed as a vampire, a gypsy, and a Ghostbuster. (TOS novel: The Rise and Fall of Khan Noonien Singh, Volume 1)
- TOS episode: "Catspaw"
- TNG episode: "The Big Goodbye"
- ST novel: Excelsior: Forged in Fire
- TOS novel: Bloodthirst
- TOS - The Eugenics Wars novel: The Rise and Fall of Khan Noonien Singh, Volume 1
- TOS comics: "The Haunting of Thallus!", "... Like a Woman Scorned!"
- DS9 novel: Station Rage
- DS9 novelization: Trials and Tribble-ations
- DS9 - The Dominion War novelization: ...Sacrifice of Angels