A relative clause is a special type of subordinate clause that gives more information about the noun that comes before it.
I threw the ball to the boy who was wearing a blue coat.
In this sentence, the underlined part is the relative clause. It tells us more about the boy. There might have been lots of boys, but only one of them was in a blue coat.
In the next sentence the relative clause gives us information about the town.
In the town where I live there is an ancient castle.
Relative clauses often begin with words such as who, which, where, when, whose and that. These are called relative pronouns.
In this worksheet you can practise identifying relative clauses and relative pronouns.