Information architecture is the design of a product's content structure: what lives where, what it is called and how users reach it. Good architecture makes everything feel like it is "exactly where it should be".
Information architecture (IA) governs three things: organisation (dividing content into sections), labelling (names users understand, not the company's jargon) and navigation (paths to content – menus, search, contextual links).
Classic IA sins: a structure mirroring the company's org chart instead of the customer's logic ("Post-Sales Process Department" instead of "Returns"), catch-all categories ("Other"), jargon labels.
Working tools: card sorting, tree testing, on-site search analysis. In website and store projects we design IA before any visuals – because no design can save a structure where nothing can be found.