Normalization involves a series of rules. The second rule is that all data must depend on the table's entire primary key. You should not have fields in a table that only depend on part of the primary key.
For instance, here is a table of student grades:
The implication of the second rule is that each table should be about a single subject. Put students in a table of students. Put courses in a table of courses. And, put grades in a table of grades. Don't co-mingle all three things in a single table. (Drinking is legal if you are old enough. Driving is legal if you have a license. Drinking and driving is never legal. Don't co-mingle the two activities. People can get hurt.)
A database is said to be in second normal form (2NF) if all of the tables satisfy the first two rules.