Slave

In Kyralia Series, slaves are kept by Sachakan Ashaki, some Ashaki are kind to their slaves, however it is not unusual for Ashaki to beat their slaves for minor wrongs. Slaves always prostrate in front of their masters when called.

Spoilers from "The Magician's Apprentice"

In The Magician's Apprentice, it is revealed that hundreds of years before the events of The Black Magician Trilogy, it was custom for Kyralian magicians to draw magic from their apprentices. This is in contrast to the Sachakan's practise of using slaves as a source of magical power. During the Sachakan War, it is shown that the Sachakans are willing to resort to draining their slaves completely of power, thus killing them.

Spoilers from "The High Lord"
By the time of The High Lord, it is still normal for Sachakan magicians, as well as Ichani, to use slaves as a means of gaining magical power.

Spoilers from "The Ambassador's Mission"
Kyralia is trying to persuade Sachaka to abolish slavery.