Explain what is Information Architecture?

[Theomax]

On web page information, architecture is often referred to the structure and navigation of an entire site.

[Andrewskyler]

Information architecture (IA) lies in the websites we use, the applications and software we download, the print materials we encounter, and even the places we actually take the time.
A good IA helps people understand their surroundings and find what they are looking for - in the real world as well as online. Practical information architecture involves creating conditions for people and organizations to work to look at their structure and language in a thoughtful way.