Final answer:
A table is in third normal form (3NF) when it is in second normal form (2NF) and lacks transitive dependencies. This requires resolving dependencies where non-primary key attributes rely on other non-primary key attributes.
Step-by-step explanation:
A table is in third normal form (3NF) when it is in second normal form (2NF) and there are no transitive dependencies. To achieve third normal form in database normalization, you must first ensure that the table is in 2NF, which means it is already in first normal form (1NF), and that there are no partial dependencies of any column on the primary key. Then, to reach 3NF, you should eliminate any transitive dependencies.
Transitive dependency in a database occurs when a non-primary key attribute depends on another non-primary key attribute, which in turn depends on the primary key. For example, in a table with fields (StudentID, StudentName, DepartmentID, DepartmentName), if DepartmentName depends on DepartmentID, and DepartmentID depends on StudentID, then there is a transitive dependency. To normalize this to 3NF, DepartmentName should be moved to another table where it depends directly on DepartmentID, which would be the primary key of the new table.