Slaves can also be owned by the state, rather than individuals. Weirdly some empires had slave armies, for example. In other cases slaves have significant rights, including their own property; Roman slaves could save money and buy their own freedom (although many slaves were worked to death in mines, or used for sex, so it was definitely still shit). In some cultures children of slaves were free (technically, although still starting from a terrible position). There was also indentured servitude, where you agreed to be a slave for a limited time period - a lot of people came to the Americas for free, but were slaves for a few years in exchange (before Europeans started buying chattel slaves from Africa, which gave better return on their investment, as long as you didn’t mind being evil).