Shedroff's definition gets things started: "Experience design is an approach to design, and you can use that approach in pretty much any discipline—graphic design or industrial design or interaction design, or retail design. It says the dimensions of experience are wider than what those disciplines normally take into account. And if you think wider—through time, multiple senses and other dimensions—then you can create a more meaningful experience."
And he follows it up with the 5 levels of significance:
1. Function ("Does this do what I want it to do?")
2. Price ("There are lots of cars out there to get me from point A to point B")
3. Emotion ("That's where lifestyle is engaged. How does this make me feel?")
4. Identity or Value ("This is subconscious: "Would I be caught dead with this?; am I a Nike fan, or an Adidas fan?")
5. Meaning (Not "Is this me?", but "Does this fit my reality?" "Does this even fit inside the world as I perceive it?")