The persona represents your public image. The word is, obviously, related to the word person and personality, and comes from a Latin word for mask. So the persona is the mask you put on before you show yourself to the outside world. Although it begins as an archetype, by the time we are finished realizing it, it is the part of us most distant from the collective unconscious.
At its best, it is just the "good impression" we all wish to present as we fill the roles society requires of us. But, of course, it can also be the "false impression" we use to manipulate people's opinions and behaviours. And, at its worst, it can be mistaken, even by ourselves, for our true nature: Sometimes we believe we really are what we pretend to be!