Manumission and abolition are both used to mean "freeing slaves" or "a release from slavery." More specifically though, manumission is the act of a slave owner setting slaves free, while emancipation (and abolition) involve government action.

What does manumission mean?

: the act or process of manumitting especially : formal emancipation from slavery.

What is an example of manumission?

A notable example is that Athens liberated everyone who was present at the Battle of Arginusae (406 BCE). Even once a slave was freed, he was not generally permitted to become a citizen, but would become a metic. The master then became a prostatès.