A relative clause gives more information about someone or something.
Some relative clauses refer to a whole sentence. Some relative clauses refer to a noun. There are two kinds of relative clauses that refer to a noun: defining and non-defining.
Defining relative clauses give information that is necessary in order to understand who or what is being referred to.
Non-defining relative clauses give extra information that is not necessary in order to understand who or what is being referred to.
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