Clauses carry different names for a reason. For example, an independent clause has a subject-verb set and can stand on its own, whereas a subordinate clause, while it also has a subject-verb set, starts with a subordinator (also called a transitional word; Click here) and so cannot stand on its own. For example,
Independent clause: I went to the store.
Subordinate clause: Although I went to the store, ...
Clauses are named according to their function. So, for example, a relative clauses "relates" to a noun; it modifies it, adds more meaning to it; e.g., The man who wants you is over there. Relative clauses begin with a relative pronoun; Click here. Those clauses can be either defining and non-defining:
Defining: A suitcase that has no handles is useless.If we omit the relative clause that has no handles, the resulting sentence is rendered semantically awkward:
Ex: ?A suitcase is useless. Defining relative clauses define the noun they modify. Without the clause, the noun loses its meaning.
Here's an example of a non-defining clause:
Non-defining: The car in the garage, which (by the way) belongs to my friend, is fabulous.Take away the relative clause set in commas and the primary meaning of the sentence stays the same: The car in the garage is fabulous. Non-defining relative clauses are easy to spot: all you have to do is add in "by the way".
The same holds true for adjective clauses and adverb clauses: they're named according to their function.
Azar is a great series. They're fabulous grammarians.
All the best.