The definition of Galley will vary from freelance writing to traditional writing for publishing books. In the case of magazines, the galley is the final page in which look of article is given more importance such as paragraph breaks, typeset, headlines, lede or very near forerunner of last page (such as photos).
You can see few variation of this particular word in case of book publishing such as page proof or galley proof. The variations are for appearing on one big block for making fast corrections. This is for making representations in final printing process. It is also known as page proof or galley proof.