A penetration test is exactly what it sounds like: authorized experts attempt to break into your systems the way a real attacker would, so that the weaknesses they find can be fixed before a criminal finds them. It is one of the most direct ways to know whether your defenses actually work.
In a penetration test, skilled security professionals, sometimes called ethical hackers, probe a system for vulnerabilities and then attempt to exploit them, chaining weaknesses together the way a real attacker would to see how far they can get. The result is a report describing what they found, how serious each issue is, and how to fix it, prioritized by real-world risk.
A penetration test is more than a vulnerability scan. A scan is automated and lists known weaknesses; a penetration test adds human ingenuity, actually exploiting and combining issues to demonstrate real impact. A scan might flag an open door; a pen tester walks through it and shows what is on the other side. Both have value, but the pen test reveals what an adversary could actually do.
Penetration tests are often required by frameworks and enterprise customers, and are wise before launching a sensitive system or after major changes. The point is not to pass a test but to find and fix the real gaps, and to repeat it periodically, because systems and threats keep changing. A clean report is only meaningful if the testing was genuine.
Better found by your tester than by their attacker.
This is general educational information, not specific security, compliance, or legal advice for your systems.