Question

What is a working title?

Answer 1

A working title, sometimes called a production title, is the temporary name of a product or project used during its development, usually used in filmmaking, television production, novel, video game, or music album.

Answer 2

A "working title" is a title by which an author or a movie director
can refer to his work in progress, with the understanding that they
don't intend for that to be the title of the final product, and that
it'll definitely change before it goes out to the public. 

That way, they don't have to keep calling it "the book I'm writing" or
"the movie I'm working on". Instead, they can talk about "Cover to Cover"
or "Thirty Frames a Second", even though those are crummy titles.