This is the 3720th most frequent Polish word.
który
"Który" means "which" or "who" in English, depending on context.
In this sentence, 'który' is used as a relative pronoun to introduce a clause providing additional information about 'dom' (house).
To jest dom, który kupiłem.
This is the house which I bought.
Here, 'który' functions as an interrogative pronoun to inquire about a choice among a group of movies.
Który film chcesz obejrzeć?
Which movie do you want to watch?
In this example, 'który' is used as an interrogative pronoun within an indirect question, asking for specific identification of the tram.