A relative clause is a clause which tells us more about a noun or a noun phrase. There are two types, defining and non-defining. Defining add essential information to tell us what we are talking about, non-defining add extra information.

Example
‘They demolished the house where I used to live' is an example of a defining relative clause.

In the classroom
Effective activities to practice relative clauses include writing definitions for crosswords and competitions to make sentences as long as possible.