What do you understand by the terms Primary Key and Degree of a relation in relational database ?

A primary key is a set of one or more attributes that can uniquely identify tuples within the relation. The primary key is non-redundant, meaning it does not have duplicate values in the same relation, and non-null attribute, meaning a null value cannot be inserted into it.

The number of attributes in a relation is called Degree of a relation. A relation having 3 attributes is said to be a relation of degree 3. Similarly, a relation having n attributes is said to be a relation of degree n.