Prime Attributes also referred as Key attributes. Similarly Non Prime attributes also called as Non Key attributes.
Prime or Key Attributes:
Attributes of the relation which exist in at least one of the possible candidate keys, are called prime or key attributes.
Non Prime or Non Key Attributes:
Attributes of the relation which does not exist in any of the possible candidate keys of the relation, such attributes are called non prime or non key attributes.
In order to distinguish whether an attribute of the relation is prime or non prime, we should always find all the possible candidate keys of the give relation.