This is the 14th most frequent Spanish word.
sus
"Sus" means "their," "his," "her," or "your" (formal), indicating possession.
Here, 'sus' again acts as a possessive adjective, with its meaning derived from the conversation context to specify ownership.
¿Dónde están sus llaves?
Where are their/his/her/your keys?
In this example, 'sus' clearly refers to the backpacks owned by 'them' (ellos), highlighting plural third-person possession.
Ellos buscan sus mochilas antes de salir.
They search for their backpacks before leaving.
In this sentence, 'sus' is used as a possessive adjective referencing the books belonging to 'them', 'him', 'her', or 'you' (formal), depending on the implied subject.