Here's the start of a subjective Usability Glossary.
Information Architecture. Think of it this way: You are building a community center. You want to make sure to build enough bathrooms to accommodate everyone, that the meeting room for seniors is on the ground floor for maximum accessibility, that you put the computer room on the side of the building with the least light.
The Information Architect designs the "blueprints" for this virtual "community center", a place that will become the foundation for your community to gather.
