This is the 5th most frequent Romanian word.
care
"Care" in Romanian means "which" or "who."
In this sentence, "care" is used as a relative pronoun introducing the subordinate clause that modifies the noun 'cartea' (the book).
Cartea pe care o citești este foarte interesantă.
The book that you are reading is very interesting.
Here, "care" serves as a relative pronoun to introduce the relative clause that describes 'oamenii' (the people).
Oamenii care locuiesc aici sunt prietenoși.
The people who live here are friendly.
In this example, "care" is a relative pronoun that connects the relative clause to its antecedent 'tema' (the topic).