I have used working drawings at school in my DT lessons! from memory my understanding is that a working drawing is a sort of technical drawing of a product (or architecture). They are used before the final build as a final constructed drawing, Usually showing different views of the design (front, back and sides, top, bottom) in order to help aided the build.
The drawing should be accurately drawn to a scale such as 1:2 (if the drawing is half the size of the actual) and 1:3 (if the drawing is a third the size of the actual)