410 Gone
410 Gone is a server's reply saying a page has been removed on purpose and won't be coming back.
410 Gone is the reply your server gives when a page used to exist and has been removed for good. Where a 404 error only says "not found," a 410 says "this was here, and it's gone on purpose." Mozilla's page on 410 Gone describes it as a removal that's likely to be permanent.
It's a small technical choice, but it's useful when you clear out old pages and want to be clear with crawlers about what you meant.
410 or 404?
For search, the difference is smaller than many people think. Google's guide to HTTP status codes groups 410 with the other 4xx errors: Google doesn't index pages that return them, and it drops pages it had once they start. So a 410 won't hurt you, and it won't do much more than a 404 would.
Where a 410 helps is with people. Your team, your agency and anyone reading your server logs can tell a page you deleted on purpose from a page that broke by accident.
When to use it
Use a 410 when a page is gone and nothing replaces it. If there's a newer page that does the same job, send people there with a 301 redirect instead, so the links pointing at the old page still lead somewhere.
For example, Fernhill Coffee retires a limited-edition blend it sold last winter. It won't sell it again, and no other blend is close. Its product page returns 410. But its old "summer cold brew kit" page redirects to the new kit, because that's what visitors to the old page wanted.
410s and AI answers
AI bots can't read a page that returns a 410, so it drops out of what they can use. That's the point when you remove something on purpose, such as an old offer you don't want answers to repeat. Remember that AI platforms may still remember a page they read before, so removing it doesn't instantly change what answers say.