ses

Ses is the plural third-person possessive adjective in French, covering "his", "her" and "its" before any plural noun, masculine or feminine: ses cousins (his/her cousins), ses idées (his/her ideas). Like every French possessive, it agrees with the thing possessed, not the owner; the gender of the person who owns the cousins is invisible in the form, and context has to do that work.

In the plural the masculine/feminine distinction collapses, so son and sa both become ses. The final s is silent on its own but links as a /z/ when the next word starts with a vowel: ses amis sounds like sez-amis. The parallel plural forms are mes (my) and tes (your, informal); the longer-distance set is nos, vos, leurs. See the French possessives guide for the full nine-form table.