The Film Yap Lexicon is comprised of terminology for certain cinematic phenomena that occur often enough to form discernible patterns — typically events or circumstances that are patently ludicrous to customs of narrative or known science and, on occasion, the result of misguided choices by filmmakers. Although these terms could take their name from numerous films, they are principally derived from the prime examples of this phenomena.
"The Big Boo" is a common trait of horror films — more specifically, PG-13-rated horror films — in which the villain reveals him/her/itself suddenly for a scare moment. However, in "The Big Boo," the villain's appearance is completely innocuous and does nothing to advance the story, existing only for the purpose of scaring the audience. Often, the characters in the movie are unaware of the villain's presence altogether and the scene does not end with any sort of actual horror.
The egregiousness of "The Big Boo" centers around the motivation for including this empty scare: It exists as a smokescreen and is often a cheap effects moment designed to mask the fact that the script doesn't have an effective scare that fits in the story. Thus, the filmmakers instead insert an effects shot accompanied by a sudden musical cue designed to startle, rather than truly scare, the viewer. It is a lazy, cheap device that detracts from the quality of a horror film.
Films like "Mama," "One Missed Call," and "Insidious" have all made liberal use of "The Big Boo." Note that "The Big Boo" is similar to, but not always the same as, a typical red herring scare, which is a device of misdirection that typically pays off (i.e., in a slasher film where a cat leaping into frame startles a character who then does not see the villain approaching from behind).
What other movie employ "The Big Boo"? Comment below and offer your own entries to the Film Yap Lexicon at lexicon@thefilmyap.com!