What Is a Galley in Magazine and Book Publishing?
Galleys mean different things when writing for a magazine (whether it's a one-time gig or ongoing work) than writing for a book publisher. The definition of a galley may even vary a bit in the traditional book publishing sense of the word. But let's look at magazine writing first. When writing for a magazine, a galley is the page that is either the last page of how your article will look (including typeset, paragraph breaks, lede, and headlines) or, it is a very close version of the final page (perhaps without photos, for example).
In book publishing, you may find some variation with regards to the definition of what a galley actually is. For example, a galley proof is the preliminary version of a publication meant for review by authors, editors, and proofreaders. These galleys are created for proofreading and copyediting purposes but may be used for promotional and review purposes as well. A page proof, on the other hand, is created in a near-final version and assumes that mistakes have been corrected. That's because correcting errors at this stage of production is expensive. These pages are a much more actual representation of the final printing.