This is the 284th most frequent Czech word.
kterého
"Which" or "of which" (masculine singular, genitive case).
Used to introduce a relative clause referring to the object of the verb 'met'.
To je student, kterého jsem potkal včera.
This is the student whom I met yesterday.
Used in a relative clause as the object of the preposition 'to' referring to a city.
Nevím, do kterého města pojedeme.
I don't know to which city we will go.
Used in a relative clause as the object of the preposition 'about' referring to the book.