Regression testing is re-running functional and non-functional tests to ensure that previously developed and tested software still performs as expected after a change. Wikipedia

A software testing method which seeks to uncover regression bugs Wikipedia Disambiguation

Checking whether changes to software have broken functionality that used to work Wikidata

Any type of software testing which seeks to uncover software regressions. Such regressions occur whenever software functionality that was previously working correctly stops working as intended. Typically regressions occur as an unintended consequence of program changes. OmegaWiki

Testing a program after a modification to ensure that areas that should not be affected by the update behave as they did in previous versions. Wiktionary