Mcguffins

A macguffin is an object or device in a film or a book which serves merely as a trigger for the plot.  It is also seen as something that 'the major players in the story are willing to do and sacrifice almost anything to obtain it, regardless of what the macguffin is.'  It is seen as something that is generic, ambiguous and completely unimportant to the plot.  Examples of macgiffins are money, power or victory.

In some thrillers the macguffin is important at the start of the plot but as the story progresses and by what the characters go through its importance to the story declines.  It may become important again during the climax of the plot however by the end of it, the macguffin is completely forgotten about. It is something that the audience doesn't care about and is totally unimportant to them.  

Examples include the brief case in Pulp Fiction.  It is what drives the plot but is mostly forgotten about in almost every scene.

Also, the Ark of the covenant in Indiana Jones.