Regression Test
In plain terms
A test that confirms new changes didn't break existing behavior.
Going deeper
Regression tests re-check previously working features after updates, catching unintended side effects. Automating them lets teams change code confidently.
Under the hood
Automated regression suites guard against reintroduced bugs; selecting which to run (impact analysis) keeps feedback fast as the suite grows.
Examples
Re-running the full suite on each release, golden-master/snapshot tests, bug-fix tests.
Think of it like...
Like re-checking that the lights and plumbing still work after renovating one room of the house.