In order to give a accurate definition of this topic, I looked it on internet and I found the next definitions on Cambridge Dictionaries Online website:
Defining relative clauses.
"We use defining relative clauses to give essential information about someone or something – information that we need in order to understand what or who is being referred to. A defining relative clause usually comes immediately after the noun it describes."
Non-Defining relative clauses.
"We use non-defining relative clauses to give extra information about the person or thing. It is not necessary information. We don’t need it to understand who or what is being referred to."
Teacher gave us these 4 examples
1) His wife, who is a lawyer, is filing for divorce
2) His wife who is a lawyer is filling for divorce
3) The students, who passed the exam, had a party
4) The students who passed the exam had a party
We can notice that in examples 1 and 3 there are comas. The use of comas is similar to use parenthesis and are used for give an extra information that we can eliminate. So, an easy way to distinguish non-defining relative clauses is using comas.
On the other hand, in the examples 2 and 4 we didn't use comas, because we're defining the subject of a universe of subjects. I.e. defining relative clauses don't use comas (or parenthesis).
We had to give an example and this was my example:
"My laboratory partners who are studying a Master's degree have a lot of courses as part of their program"
In this example, I'm defining only my laboratory partners who are stydying a Master's degree. It means I have more partners who, for example, are studying a PhD degree.
Later, we learned that we can use a relative pronoun to introduce a defining relative clause
Where - For places
Who - For persons
That - For someone
Whose - correlation of possesive
Which - for objects



















