Simply, a persons' personality is all of those traits and characteristics which they act on and have but which they did not choose to act on or have.
This is not the standard meaning of the word. However I think when one believes that self-change and growth and improvement are all valuable to pursue, and one also believes that regardless of the nature and nuture debate as to the source of many non-chosen traits and characteristics and beliefs (etc), it follows that the essential dividing line about a person is which and how many of their traits and characteristics and beliefs are there because they put them there. Many people, hereinafter called the sheep, did not choose any of these things for themselves. These are people who each found that for some reason (or perhaps its the default we're born with though I don't think this is true) the church, the state, the family, the neighbours, the schooling, the job, the peer-group / friends and television commercials were sufficient sources of world-view that they did not alter any of the package deal. This is not the time for me to discuss how this creates wonderful cannon-fodor for both war and industry.
Personally, for a while I tried to minimize the amount of personality I had. For a long while actually. This didn't make me less interesting, I suspect since I wasn't entirely successful. But after awhile of this, I decided that a few chosen bits of personality were desirable in the abstract - they give a person worldly anchors. So Peter plays Moira Dungeon a lot, and I like.. nice clothes.
But just try to get a non-abstract opinion out of me!