How would you explain content management system to a client?

I tell them it's the back office of the website. They log in, type into boxes a bit like a Word doc, hit publish, and the page appears with the design already applied - no developer needed to change a price or add a blog post. WordPress is the one most of them have heard of. The thing to say up front is what it does NOT do: it won't write the content or keep itself updated, someone still owns that.