What's in a value?

I've been meaning to write this blog post for a long while now. I don't really know why, but it's about a realization of some importance to me. And by value I don't mean the usual "our company's values are openness, honesty and integrity" bollocks. You know, the part of the holy mission-vision-strategy-values quad that companies use as repairkit when they have lost one or - more often - all of the four.

So what is a value, for a person? Here is my definition:

A value is something a person values in her or his head that cannot, and should not, be justified or rationalized.