2 Answers

Prefix: an placed before a base or another prefix, as un- in unkind, un- and re- in unrewarding.

Post-: a prefix meaning after or later than

Here are five examples of prefixes using post-:

Postpone (verb): "She decided to postpone her vacation until next year."
Posthumous (adjective): "This is a posthumous album by Michael Jackson."
Postnatal (adjective): "There's a good sytem of postnatal care for mothers in my country."
Postdate (verb): "I'll postdate this cheque until the end of the month when I get paid."
Postmortem (noun): "They had a postmortem to find out how the wan was killed."

http://www.ecenglish.com/learnenglish/lessons/using-prefix-post

I think you may have worded this wrong. Did you mean to ask, what does the prefix post mean? If so, then the prefix, "post" would mean "after".