Defining and Non-defining relative clauses

In English there are subordinate sentences inside a major sentence and there are many sort of 

subordinate sentences, we focus now those parts of the sentences which are introduced by a

relative pronoun and these relative clauses use to describe a noun. A relative clause gives more

information about the person, animal or thing that can be essential (defining) or just informative

(non-defining) to the main sentence. They are very useful in sentences because we avoid writing two

 sentences and contributes to the fluidity of the sentence.

The most common relative pronouns are who (used instead of people), where (used for places), which

 (used instead of things), whose (used instead of possessions), we can replace that instead of who or

 which. Defining relative clauses define or identify the people, animal or thing we are referring,

 sometimes we can avoid the relative pronoun because the subject is the same as in the main sentence.

Ex. The man who is wearing a tie is my brother.

The horses which ran faster yesterday were taken to the prairie today.

Non-defining relative clauses add extra information which is non essential to the meaning of the

 sentence. They also use the normal relative pronouns such as who, where, which and whose but it is not

 used "that" in these sort of sentences. If we delete them the main sentences has meaning still, also they

 appear usually between commas or after a comma. 

Ex. The girl, whose brother waved to you, was my former flatmate.

The village of Buckingbrook, where they lived for three years was very far from the shore.