Defining expertise: more questions than answers

In a recent conversation (via blog) with Sahana Chattopadhyay,
the question of expertise came up. Sahana said:

I also believe that when we gain sufficient command over a subject, it is because we are passionate about it, have actively sought all information related to it...This kind of "passion" cannot be taught. Each person has to go through the pain and pleasure of learning to arrive at that stage. While we can impart information, we cannot make anyone an expert."

This got me thinking about the whole idea of expertise, something that I am now working on for my dissertation. Sahana later says:

You've set me thinking again...and the more I think, I feel that someone who is passionate about a subject will NEVER think/feel they are experts. They will always want to know more, will know that there is no defined end to "knowing"...there will never be a point when anyone can know it all...then, what do we mean by expertise?

This leads me to two questions that I currently am working on:

How do people define "expertise"?
How do people "use" expertise?

I still am in the preliminary stages of analyzing this question for a group collaborative writing project. However, Sahana's comment reminded me of the question I often struggle with in foreign language, when is someone "fluent"? Just as Sahana pointed out in her comment about people who are passionate about a topic never feeling satisfied that they know enough about the topic, a person who does not grow up speaking a foreign language or who learned the language through "informal means" (in other words, through their parents not at school) often feel they are not "fluent" enough.

While I can read French as well as I can English, I can converse in French and Spanish, even thinking in those languages and dreaming in them when I was immersed in the culture, I still wonder what it would be like to be "native like" and not make mistakes when I speak the language. Ironically, my colleagues used to have me proofread their Spanish (they were native speakers) because I would catch their grammatical mistakes. Yet, I have trouble telling people that I am "fluent" in French and Spanish. I am shy to post comments on the Spanish or French blogs that I read for fear that I will sound like a complete idiot.

I think the same is true for any topic that we are interested in that we did not grow up with. For example, I would say I was an expert skier (although do to a severe skiing accident 20 years ago, I can no longer do physically). I started when I was 7 years old, and was an excellent skier. My husband learned when he was in his late teens. Neither of us think of him as an "expert" (although he has never had a serious injury as I have).

So, now I wonder about the nature of expertise and what makes an "expert". Is passion necessary to be an expert? Who defines expertise: the person who is the expert or those that need the expertise? What happens when there is a difference between a person's perception of their expertise and those that are in need of the expertise? This could be that the person who is the "expert" may not conceive of themselves as an expert or those who may conceive of themselves as an "expert" may not have the expertise the others are looking for (so in the outsiders minds that person really is not an "expert"). Who defines expertise? Who defines expert? What are the parameters of expertise and expert and how are they defined? Does someone have to be an expert to teach? Is it necessary to have a passion for the subject to be an expert? What is the relationship between the designation of "expert" and "knowing how to do something"?