This is the 5th most frequent Latvian word.
kas
The Latvian word "kas" means "who" or "what" in English.
In this question, 'kas' is used as an interrogative pronoun meaning 'what' to inquire about the subject of the sentence.
Kas ir tavs mīļākais krāsa?
What is your favorite color?
Here, 'kas' is used as a relative pronoun meaning 'who' referring to the subject of the relative clause.
Man ir draugs, kas dzīvo Londonā.
I have a friend who lives in London.
In this sentence, 'kas' acts as an indirect question introduction, translating to 'what' inquiring about the clause's content.