Real Dictionary

voluntary
A voluntary worker is someone who does work without being paid for it, because they want to do it.
Voluntary work is done by people who are not paid for it, but who do it because they want to do it.
adjective: Voluntary actions or activities are done because someone chooses to do them and not because they have been forced to do them.

voluntary in American English
brought about by one's own free choice; given or done of one's own free will; freely chosen or undertaken
adjective: done, made, brought about, undertaken, etc., of one's own accord or by free choice
noun: something done voluntarily

voluntary in British English
adjective: performed, undertaken, or brought about by free choice, willingly, or without being asked
noun: a composition or improvisation, usually for organ, played at the beginning or end of a church service