I cannot tell you how many times I have seen someone confuse a vulnerability assessment with a penetration test. They are not the same thing. Not even close. And yet I watch organizations pay for one thinking they are getting the other, and vendors happily take the money without correcting the misunderstanding.
Vulnerability Assessment
A vulnerability assessment identifies weaknesses. You run a scanner against your network, it produces a report with a list of findings, and someone writes up recommendations. The end. Nobody actually tries to break in. Nobody chains vulnerabilities together. Nobody tests whether your monitoring catches anything. You get a list of theoretical problems.
This is useful. It is not a penetration test.
Penetration Test
A penetration test simulates an actual attack. Someone with skills and tools tries to break into your systems the way a real attacker would. They chain vulnerabilities. They pivot between systems. They escalate privileges. They try to access data they should not be able to reach. And critically, they test whether your people and processes detect and respond to the attack.
A good pen test tells you what actually happens when someone comes after you. A vulnerability assessment tells you what could theoretically happen based on a software scan.
Why this matters
I have seen organizations run a vulnerability assessment, fix the critical findings, and then tell their board they have been penetration tested. That is a lie, even if it is an accidental one.
If your auditor asks have you been pen tested and you hand them a Nessus report, you are going to have a bad day eventually. When the real attackers come, they do not run Nessus and go home.