IA is... def ... Try to get a summary from someone else. See if I can rope Andrew Hinton into it.
It's a whole, very involved subject area... will only touch on it, and leave out many, many key aspects. If not familiar, I encourage you to read more or just to hire an IA to do much of this for you.
* Polar bear book * Others... Understanding Context?
I bring it up because of 1) Importance, as we'll discuss below with processes, etc. and 2) Not enough UXers include deep IA understanding so tend to skip it. Pretty but useless products result.