I've been a UX Writer for over two years, and just today my mom told me, "When people ask me what you do, I don't really know what to say. Can you explain it again?" My husband likes to joke that I spend a day deciding whether a button should say "Buy" or "Buy Now." My friend recently confided to me that he thought I was writing instruction manuals. Another thought my job consisted mostly in writing blogs and marketing text.
I'm never offended; the UX world is a foggy one full of untranslatable jargon to the average outsider, and writer has so many different definitions that you may as well pick one out of a hat.
So: what do I actually do?
You can find a breakdown of how I spend my time here, but let's start with the "UX" part of my title: User Experience is just the term for how anyone who uses a product (anything from an app or website to a kettle or door) interacts with it. Are the processes understandable? Does the product do what it's supposed to, and what's expected of it? Is it easy to use? How does it feel to use?
The second part, writer, is pretty straight-forward. It's deciding the text and terminology that show up on that product: from, yes, the text on a button, to the instructions for setting up an account, to the way settings are organized.
But: my job isn't to "write some content real quick," to throw in a few words at the end of the development process. A good UX writer works alongside project managers, designers, and developers to influence how the product works. A big part of UX Writing is information hierarchy, aka the order and timing of how information is presented. Just as important is content strategy: determining a product's tone and voice, as well as standard terminology.
Being a UX Writer means being a button writer, yes, but also a content strategist, usability expert, information architect, proofreader, localization manager, dictionary creator, and so much more. It isn't about being a native speaker (some of the best UX writers aren't) or knowing basic grammar; it's about thinking strategically, and fighting for content that will make the experience as painless as possible for the user. And it's really, really rewarding.
(Hope this answers your question, Mom.)