Dictionary attack
Guessing with a list of likely passwords instead of every possible string. 'Password1' is in the book. Yours should not be.
A dictionary attack tries well-known passwords and character patterns rather than the entire keyspace. It works because people reuse and because complexity rules produce predictable shapes.
Password managers, banned-password lists, MFA, and throttling. Do not build a 'clever' scheme that is still on the first page of every list.
Fact source: ASD's ACSC glossary.