There is not a single, official definition of Fair Trade which is followed by everybody. Each organization has developed its own set of rules, which, nevertheless, are quite similar and address more or less the same issues. A good definition, as crafted by FINE in October 2001 goes like this:
Fair Trade is a trading partnership, based on dialogue, transparency and respect, that seeks greater equity in international trade. It contributes to sustainable development by offering better trading conditions to, and securing the rights of, marginalized producers and workers - especially in the South.
Fair Trade organizations, backed by consumers, are engaged actively in supporting producers, awareness raising and in campaigning for changes in the rules and practice of international trade.
Along with that definition, we may read Fair Trade's strategic intent, which is:
You may find here a bit more about this.
What I feel that Fair Trade is: a means that enables us in the economic North to improve lives on those in the South, simply by respecting and not exploiting them, by avoiding donations and allowing empowerment, by treating disfavored people as our equals. That's it.
I am most motivated when I realize that just by choosing our food or any other item wisely, we can really make a difference in our world and influence the way global economy works. As someone has put it, Fair Trade brings non-economic values, such as moral sense and honesty, into commerce.
I like especially when it says "...that seeks greater equity in international trade.". To me, this is a key point, as I see that differences between North and South are increasing daily and that Fair Trade is helping in reducing these differences.