Indentured servant: a person who signs and is bound by indentures to work for another for a specified time especially in return for payment of travel expenses and maintenance.
Slave: someone who is legally owned by another person and is forced to work for that person without pay
Now I will be the first to admit, that according to some sections of Deuteronomy and Leviticus this really does seem like indentured servitude. In fact Deutoronomy 15:12-14 states "12 If a fellow Hebrew, a man or a woman, sells himself to you and serves you six years, in the seventh year you must let him go free. 13 And when you release him, do not send him away empty-handed. 14 Supply him liberally from your flock, your threshing floor and your winepress. Give to him as the LORD your God has blessed you."
As such we could be forgiven if we thought this was indentured servitude. I should also not, this concept of indentured servitude is built on the false pretext that the Israelites were slaves in Egypt. Deuteronomy 15:15 "Remember that you were slaves in Egypt and the LORD your God redeemed you. That is why I give you this command today."
This is also the point where the line between slavery and indentured servitude disappears. As a slave is life long as it is a purchase, or a legal possession. So how are we to think about the following lines which relate to laws of indentured servants/slaves and treatment of indentured servants/slaves.
Deuteronomy 15: 17 "then take an awl and push it through his ear lobe into the door, and he will become your servant for life. Do the same for your maidservant."
Exodus 21:4, 7 and 20-21 "If his master gives him a wife and she bears him sons or daughters, the woman and her children shall belong to her master, and only the man shall go free."
"If a man sells his daughter as a servant, she is not to go free as menservants do."
"If a man beats his male or female slave with a rod and the slave dies as a direct result, he must be punished, 21 but he is not to be punished if the slave gets up after a day or two, since the slave is his property."
Leviticus 25:46 " You can will them to your children as inherited property and can make them slaves for life, but you must not rule over your fellow Israelites ruthlessly." By ruthlessly they mean, beat but don't kill.
Now stop and think.
If you have read these texts, and you still think the Bible is not supportive of slavery in all its barbaric form, then you need a head exam. Slavery was supported by the Bible and by the Christian faith until it became evident that people of other races were also people and not animals.