The Hebrew word used for slave in Exodus 21
ebed is translated, mainly, as servant by Strong's Concordance… "Most importantly, slavery was not intended as a permanent condition, but a voluntary, temporary refuge for people suffering what would otherwise be desperate poverty. “When you buy a male Hebrew slave, he shall serve six years, but in the seventh he shall go out a free person, without debt” (Exod. 21:2). Cruelty on the part of the owner resulted in immediate freedom for the slave (Exod. 21:26-27). This made Hebrew slavery more like a kind of long-term labor contract among individuals, and less like the kind of permanent racial/class/ethnic exploitation that has characterized slavery in modern times.
Also in contrast to slavery in the United States, which generally forbade marriage among slaves, the regulations in Exodus aim to preserve families intact. “If he comes in single, he shall go out single; if he comes in married, then his wife shall go out with him” (Exod. 21:3). The general equality between slave owners and slaves is highlighted by the regulations about female slaves in Exodus 21:7-11. The only purpose contemplated for buying a female slave was so that she could become the wife of either the buyer or the buyer’s son (Exod. 21:8-9). She became the social equal (as wife) of the slaveholder, and the purchase functioned much like the giving of a dowry. Indeed, she is even called a “wife” by the regulation (Exod. 21:10). Moreover, if the buyer failed to treat the female slave with all the rights due an ordinary wife, he was required to set her free. “She shall go out without debt, without payment of money” (Exod. 21:11)… (Source:
http://www.biblestudytools.com/dictionary/slave/ )