For Memory Alpha's spoiler policy, please see Memory Alpha:Spoiler policy.
A spoiler was a statement that revealed key information about a story's plot, which, if known prematurely, would "spoil" the experience for the audience.
In 2370, after initially asking who won the fictional future war between Cardassia and the Klingon Empire depicted in Meditations on a Crimson Shadow, Julian Bashir changed his mind and requested Garak not spoil the ending of the novel for him. (DS9: "The Wire")
Among D'Vana Tendi's science notes was the story of how she reorganized The Dog's mitochondria. She wasn't going to share any spoilers with Brad Boimler, Beckett Mariner, and Sam Rutherford yet, but she promised the story was "super funny". (LD: "Much Ado About Boimler")