Non defining : As the name suggests, non-defining relative clauses tell us more about someone or something, but the information in these clauses does not help us to define what we are talking about.Take for example the sentence: Gorillas, which are large and originate in Africa, can sometimes be found in zoos. In this sentence we are talking about all gorillas, not just some of them. The information in the non-defining relative clause tells us something more about gorillas in general. It does not define a small group of gorillas or an individual gorilla. If the non-defining relative clause were removed from the sentence, the sentence would still be gramatically correct and the meaning would not have changed, although we would have less detail.
Defining : 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.