|su||sus||his, her, its, their, your (formal)|
Forms and Uses
The possessive determiners, also called possessive adjectives, serve to express ownership or possession (hence the name).
Possessive adjectives, like all adjectives in Spanish, must agree with the noun they modify. Thus, if the noun is feminine, the possessive adjective must be feminine, too. However, in Spanish the masculine and the feminine forms of the possessive determiners mi, mis, tu, tus, su, and sus are the same. In the following example, the singular masculine noun dinero uses the form nuestro, while the feminine plural noun cosas requires the form nuestras.
Nuestro dinero, nuestras cosas, valían menos aquí en los Estados Unidos.
Our money, our things were worth less here in the United States.
Note that su has many potential translations in English: his, her, its, your (formal), or their. So, how do you know which meaning is intended? Context! In the following sentence, since su refers to mis padres, we know that su means their.
Mis padres decidieron hacer su propia casa.
My parents decided to make their own house.