A hotfix is a fix to an issue that has been discovered on production that needs to be fixed and go live ASAP.
Usually a hotfix takes priority and it will be deployed to the test environment. Testing and verification of the hotfix is guided by a checklist that could reside either on the issue or the corresponding pull request. Once fix has been verified, smoke tests are then run guided by the smoke testing suite for platform. Once these tests pass, then the hotfix is merged into production.