This is the 13th most frequent Bulgarian word.
който
"Който" means "who," "which," or "that" (relative pronoun).
The word 'която' (the feminine form of 'който') introduces the relative clause and refers to the feminine noun 'книга'.
Има книга, която искам да прочета.
There is a book that I want to read.
The phrase 'за която' is a prepositional relative pronoun form of 'който,' connecting 'работата' to its related clause and indicating the relation defined by 'за.'
Това е работата, за която си мечтал.
This is the job that you have dreamed about.
The word 'който' functions as a relative pronoun, referring to 'човекът' and connecting the main clause with the relative clause.