What is a vulnerability scan, and how is it different from a penetration test?

A vulnerability scan is an automated check that probes a system - a website, a server, a network - against a database of known weaknesses and misconfigurations, and reports what it finds. It is the routine, repeatable health check of security: fast, broad, and run regularly:

• Scan vs pen test - a vulnerability scan is automated and tells you “here are the known issues an attacker could look up”; a penetration test is a human expert actively trying to break in and chain weaknesses together, and it is priced accordingly.
• A certification expectation - the audited Platinum tier of the SMB1001 standard expects regular vulnerability scanning of internet-facing systems.
• The realistic small-business layer - regular scanning of the parts of your site the public can reach is the realistic, affordable layer - the continuous health check - while a full penetration test is reserved for when a contract specifically requires it.

A vulnerability scan is the regular automated health check; a penetration test is the occasional expert break-in attempt - most small businesses need the first far more often than the second.