Blank lines inserted into a message posted on the Internet so that the reader can choose whether or not to scroll down and read a spoiler.

plural of spoiler effect

Used other than figuratively or idiomatically: see spoiler, alert: a warning that plot elements in a drama will be exposed.

An indication, placed in a text, that the plot of a drama is about to be exposed / Indicates that the speaker is about to reveal something unanticipated or unpleasant

Synonym of Q-switch