You mean they are relative adverbs. However, some Grammar Guide states they are subordinators or conjunctions.
Is the difference due to the different grammarians' standpoints?
This is the terminology I tend to follow:
is a large group of words that serve to join words, phrases or entire clauses. The group has three sub-types based on form-class
(and not connective types). These are: conjunction, connective adverb, connective pronoun.
This means three parts of speech can join clauses and sentence constituents. Prepositions or interjections, for example, can't.
embraces the two categories coordinators
(and, or, but, etc.)
FANBOYS. It is an acronym that is used as a mnemonics to recall the types of coordinators. Y = yet.
I think the inventors of the acronym used a different terminology from that which I use. 'Yet' is an adverbial conjunct in my book, one of the four types of adverbials.
(while, although, because, unless, etc)
I have always though that only subordinators can introduce subordinate clauses. This is not true. Look at this sentence:
We are proud of you despite WHERE you are living now.
The whole sentence is the matrix clause or superordinate clause. 'despite' is a preposition. What follows 'despite' is a sentence constituent: a prepositional complement. How is this constituent realized? A subordinate clause is embedded into the superordinate clause. Why subordinate? Because it plays a sub role. Sub role how? It realizes part of the matrix clause. 'Where' in the sentence is a connective adverb and not a subordinator.
There is a gradience running through between the class of coordinators and subordinators, which means there are instances of conjunctions that are not clear-cut between coordinator and subordinator? Why not clear-cut? Because the two categories have distinct features and these linking words looks like hybrids. It is not within the scope of our present considerations, so I am not going into it in detail.
2. Connective adverb
This is the second sub-group of fconnectors. The group of Connective adverbs has several sub-types. These are:
(a) Adnominal conjunctive adverb
This was the time when we first met.
The bolded part plays a subordinate role because it specifies 'the time'. It describes 'the time' so it has adnominal (not nominal) function. 'when' is relative because it relates to its antecedent. 'the time'. Cool.
(b) Nominal conjunctive adverbs
where I am = 'This'; subjective complement --> subordinate; nominal
(c) Adverbial conjunct
These are, however, all the same, nevertheless, etc. They provide a semantic link between clauses.
(d) Conjunctive adverbs
They are interrogative adverbs used to introduce embedded questions.
He asked me how I did.
He asked where I am.
He asked why I came.
3. Connective pronouns
(a) Relative adnominal connective pronouns
I do not they guy who is standing over there.
'who' is part of 'who is standing there'. 'who is standing there' modifies 'the guy', hence adnominal (non-nominal, adjectival). Connective, because it connects the sub-clause to the rest of the matrix clause. Pronoun, because 'who' is a pronoun. Adnominal connective pronouns usually have an antecedent.
This is the time that we die.
-- that we die = adverbial and not adjectival --> non-nominal --> adnominal; that = connective pronoun
(b) Relative nominal connective pronoun
Relative nominal connective pronouns do not have an antecedent.
(c) Conjunctive connective pronoun