Mitch didn't know whether she was referring to her job or their relationship.

It most often refers to the relationship between the action and the subject in the sentence.

She didn't like it when he referred to their relationship in such a casual manner.

They may refer to the relationship with the person.

The term often refers to the relationship between the entire human population and its environment, the Earth, or to smaller geographical areas such as countries.

She knew he was referring not only to their professional relationship but their personal one, as well.

The lyrics refer to the couple's relationship as their "dirty little war."

A paternal bond refers to the relationship between a father and his child.

A news article uses the word 'bestiality' three times in referring to their relationship.

The first is a "substantive meaning" that refers to the relationship humans have with one another and to the earth.