What the heck is a MacGuffin?

What the heck is a MacGuffin?

According to Oxford: Mc·Guf·fin /məˈɡəfin/ noun noun: MacGuffin an object or device in a movie or a book that serves merely as a trigger for the plot. “the McGuffin in this intriguing comedy is an unpublished novel by a young writer killed in the war”...