"referencedColumnName" property is the name of the column in the table that you are making reference with the column you are anotating. Or in a short manner: it's the column referenced in the destination table. Imagine something like this: cars and persons. One person can have many cars but one car belongs only to one person (sorry, I don't like anyone else driving my car).
Table Person
name char(64) primary key
age intTable Car
car_registration char(32) primary key
car_brand (char 64)
car_model (char64)
owner_name char(64) foreign key references Person(name)
When you implement classes you will have something like
class Person{
...
}
class Car{
...
@ManyToOne
@JoinColumn([column]name="owner_name", referencedColumnName="name")
private Person owner;
}
EDIT: as @searchengine27 has commented, columnName does not exist as a field in persistence section of Java7 docs. I can't remember where I took this property from, but I remember using it, that's why I'm leaving it in my example.