Slaves are a variation of Manpower, but signify an enslaved or forced workforce. The Slaves resource can be used instead of Manpower in certain circumstances like as part of a labor force (Mine or Industrial Complex) and in certain military usage.
Slaves used in labor have an increased chance of revolt (+15%) compared to a traditional workforce (standard Manpower).
Slaves can also be sold and purchased on the Black-Market.
Slaves can be created via Cloning technology.
Slaves can also be captured during raids on cities, or turning captured prisoners (soldiers/crews) into slaves instead of keeping them as prisoners.