What is the difference between a "prisoner" and a "slave"?

I would of thought that a prisoner has a sentence to serve then is free. but a slave will never be free

Simply put, a slave is considered property, a prisoner is not

A slave is a person who is the property of and wholly subject to another; a bond servant.

https://www.dictionary.com/browse/slave

A Prisoner is a person who is confined in prison or kept in custody, especially as the result of legal process or of war.

https://www.dictionary.com/browse/prisoner

A prisoner and a slave may find themselves in similar circumstances of servitude, but a slave has no reasonable expectation of ever being free because he/she is inhumanely viewed as "property." The US Constitution bans slavery, except for those who are in prison. Therefore prisoners are also held in conditions of slavery, of forced labor and bondage, not simply "confinement."