A student in a pesantren is called a santri. After the founding kyai of a pesantren dies, his son or another santri may take over the supervision of the school, and would then be called kyai. It is possible for a large boarding school to have several kyai living and teaching there.
A student in a pesantren is known as a santri. Upon the death of the founding kyai, his son or another santri might assume responsibility for managing the school, becoming a kyai themselves. It's possible for an extensive boarding school to have several kyais living and teaching there.