What is the difference between the second normal form and the third when talking about databases?

Question

If I understood it right second normal form means that there is no attribute dependent on a primary key, which is not important for the attribute. But I do not understand the third form. Could anyone please help me out? Thank you!

Answer 1

A relation is in third normal form if it is in second normal form and it does not have any transitive dependency i.e It contains only columns that are non-transitively dependent on the primary key.
Now transitive dependency can be explained as follows:
Say, we have the functional dependencies of attributes A,B,C ( A is the primary key) as
A->B (B depends on A) and
B->C (C depends on B) then we can say that A->C (C depends on A)