What does "for finished artwork" mean?
A 'finished' artwork is a piece that has been worked to a particular level of detail.    There are various levels of 'finish' from a basic outline to a 'finished' sketch, then from a basic drawing to a highly 'finished' piece of work.
To give an example, an artist might do a rough sketch of an idea and then a more detailed sketch or a colour sketch or even create a study for the whole piece or just a small section of the entire drawing/painting.  From that he/she might create a 'finished' piece for exhibition.  The sketches and studies might be made on cheap paper or canvas (sometimes on the back of an envelope)  but the 'finished' piece would be made on the best quality paper/canvas etc. So in the context of your Bristol board, it is a high quality paper that would be used for 'finished' artwork.  You could make sketches and transfer them to you good quality paper or you could draw directly onto it, it is your choice.