This continues to be a hot topic in Web Development, and by just broaching the subject, I risk the wrath of people in my field who may disagree with the answer I am going to try and outline in this article. IA, as it is referred to, overlaps with other aspects of project planning, and often blurs the lines between itself and information design, project management, usability analysis and user-experience approaches.
For example, James Kalbach gathers a few definitions in his article "IA, Therefore I Am":
"Definitions range from Elaine Tom's 'a map of the underlying information structures' to Wurman's 'the building of structures that allow others to understand' to Rosenfeld and Morville's 'the combination of organization, labelling, and navigation schemes within an information system' and John Shiple's 'the blueprint of the site upon which all other aspects are built - form, function, metaphor, navigation and interface, interaction, and visual design.'"
The purpose of this article is to supply clients with a basic understanding of what someone with the title 'Information Architect' normally offers in their skill set, and try to clarify what their role is on a development team.