Relative clauses give us more information about nouns. For example, they might tell us about one in a group, or what kind of noun we are talking about. There are two kinds of relative clause: identifying and non-identifying.

Identifying relative clauses tell us which one we are talking about:

Glen is a piano player who wrote my favourite song. (Other piano players did not write my favourite song, and none of these players are named Glen.)

Do you have a dessert that two people could share? (Some desserts cannot be shared, but I am not interested in these desserts.)

Students who study every day get the highest scores on tests. (To get the highest scores on their tests, students should study every day.)

Non-identifying relative clauses just add extra information about the noun:

Solomon, who plays guitar, works in Victoria.

Many students study at the library, where you have to be quiet.

Non-identifying clauses are more formal, and are usually separated from the main clause by commas. Identifying clauses cannot be removed without changing the meaning of the sentence, but non-identifying clauses usually can be removed without changing the meaning.