Definition:
A Release Candidate(RC) is a beta version with potential to be a final product, which is ready to release unless we find any significant bug. Release Candidate is also known as “going silver”. A release is called on code complete when the development team agrees that no new code will be added to this release at this stage and product is stable with agreed features designed, coded and tested through multiple beta cycles with no showstopper bugs. Testing is conducted at the customer locations from user’s perspective using the release candidate as though it is a finished product.
Release candidate has few issues when compared to the Beta testing build. Release candidates are not for production deployment but are for testing purposes only, however there is no difference between the final build and the last release candidate. Installation issues are verified for final time, critical workflow test is performed against the release candidate. Automated regression test is recommended to done against every release candidate. A team can use a checklist to evaluate each release candidate which includes all features that provide business value for the release, meeting all build acceptance criteria, has proof of having passed all agreed upon test, has no open defect reports.
Further Reading:
Book: AGILE TESTING A Practical Guide for Testers and Agile Teams
https://en.wikipedia.org/wiki/Software_release_life_cycle#Release_candidate
https://www.tutorialspoint.com/software_testing_dictionary/release_candidate.htm