A metaphor-driven design discipline concerned with the learnability, usability, and conceptual integrity of information systems.
Information architecture uses the metaphor of architecture (as in the design of buildings, parks, or museums) to explain concepts of information organization and inspire new theories and approaches.
Information systems include any “thing” with an underlying conceptual model. In UX and product design work, these things tend to be apps, digital products (SaaS apps), and websites.