This is the 4722nd most frequent German word.
weiss
"Weiss" means "white" in English.
Here, 'weiß' is the first-person singular form of the verb 'wissen', which means 'to know'.
Ich weiß die Antwort auf die Frage.
I know the answer to the question.
Here, 'weiß' is an adjective describing the color of the shirt as white.
Das Hemd ist weiß.
The shirt is white.
In this sentence, 'weißt' is the second-person singular present tense of the verb 'wissen', used to ask if someone knows the location of the book.