This is the 326th most frequent Spanish word.
tus
"Your" (possessive, plural).
In this sentence, 'tus' is used to express possession in the second person singular (informal) for multiple objects (books).
Aquí están tus libros sobre historia.
Here are your books about history.
Here, 'tus' indicates possession related to 'amigos' (friends), again in the second person singular informal form for plural nouns.
¿Tus amigos ya llegaron a la fiesta?
Did your friends already arrive at the party?
The word 'tus' expresses possession of 'ideas' (ideas) belonging to the person being addressed informally.