Selected answers from the Dumb SEO Questions G+ community.
E Dieter Martin: That`s most likely your CMS who`s generating those URLs. Make sure you have a proper canonical tag for your primary page. Wordpress does this often, but if I am not mistaken, the SEO plugins there are able to even set those additional pages to "noindex".
Michael Martinez: The "?s" fragment is used to indicate a search results sequence in some CMS`s. In WordPress that would result in a page description looking like this: "some number SEARCH RESULTS FOR ``"
Michael Stricker: Some search plug-ins, add-ons or embedded on-site search apps may do the same, or an over-zealous CMS that insistently resolves any URL to a 200 status, even if it must gin up a new page to land on. Noindex them as they’re written. In the past I’d have said use URL Handling in GSC to advise Google they are dupes.