Card Sorting

Card sorting is an exercise where you hand people a stack of labeled cards, each one a topic or page, and ask them to group the cards in ways that make sense to them. Watching how they cluster things tells you how your audience expects content to be organized.

It comes in two forms: open sorts, where people name their own groups, and closed sorts, where you supply the categories. Either way, it's a cheap, direct way to ground your information architecture in real mental models instead of guesswork.