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Samkv Wikipedia:
Release candidate

The term release candidate refers to a version with potential to be a final product, ready to release unless fatal bugs emerge. In this stage of product stabilization (read QA cycle), all product features have been designed, coded and tested through one or more Alpha cycles with no known showstopper-class bugs.

RTM

The term “release to manufacturing” or “release to marketing” (both abbreviated RTM) - also known as “going gold” - is used to indicate that the software has met a defined quality level and is ready for mass distribution either by electronic means or by physical media. The term does NOT define the delivery mechanism, it only states that the quality is sufficient for mass distribution. The deliverable from the engineering organization is usually in the form of a gold master CD used for duplication or to produce the image for the web.

In most if not all cases, RTM happens prior to general availability (GA) where the product is released to the public.