Wiktionary: (software engineering) A version of a program that is nearly ready for release but may still have a few bugs; the status between beta version and release version.

Oxford: a version of a product, especially computer software, that is fully developed and nearly ready to be made available to the public. It comes after the beta version.

I couldn’t find more definitions from “big” dictionaries, but literally no definition I’ve seen agrees with you. I wonder why that is.