This week's book giveaway is in the Other Open Source APIs forum. We're giving away four copies of Storm Applied and have Sean Allen, Peter Pathirana & Matthew Jankowski on-line! See this thread for details.
You can use joinColumn to define a join column in the table that references the primary key of the associated table. PrimaryKeyJoinColumn is a little diferent and much easier when the primary key of the related entities are identical, so you do not need to specify a join column.
A relationship mapping where one table has a reference to another table. i.e existence of foreign key column. In JPA its called join columns and @JoinColumn annotation is the primary annotation used to configure these types of columns. Eg: