Information Architecture (IA) is the practice of organizing and labeling content in such a way that it guides behavior and increases usability.
Information architecture actually goes very deep. It includes elements of metadata, SEO, archiving, user research and design, to name a few. The process of designing the information architecture of a site or app involves techniques like story-mapping and creating visual vocabulary charts. This is a communicative process where we try to understand the most important goals of the product or service, as well as the existing knowledge and assumptions of the end-user.
Does the interface of an application communicate its message? Can visitors find the information they want without help? Are visitors behaving as hoped and intended? Good information architecture makes all of these things possible.
When we refer to information architecture, we do so most often in the context of User Experience (UX). It is a critical step in the process of planning and creating beautiful, user-friendly software.