Define fetish?

i recently commented on an excellent blog posted by Goddess Serenity.
Basically the point i raised was that we need to more clearly define certain words that are very commonly used here. i would like to explore this in greater detail, specifically in regard to the word fetish.

In my comments i said that many on this site claim money as a fetish, and yet most of us love and even crave money. Especially when we don't have any.

Yet as i said i absolutely love pavlova, and health issues aside could eat a whole one every day.
Yet all i would do with said pavlova is use a spoon to convey it to my mouth and eat it, which is pretty normal.And is there anyone on this site unaware of my obsession with Doctor Who?

So my questions are what qualifies something as a fetish?
How is it different from an obsession? Does it have to have a sexual component?

What do you think?