Card Sorting.

Card sorting is a simple technique in user experience design where a group of subject experts or “users”, however inexperienced with design, are guided to generate a category tree or folksonomy. It is a useful approach for designing information architecture, workflows, menu structure, or web site navigation paths.

Card sorting
Card sortingWikipedia
OptimalSortOptimal Workshop
Improving Your Information Architecture With Card Sorting: A Beginner's GuideSmashing MagazineOctober 20th, 2014
10 Things to Know about Card SortingMeasuring UApril 3rd, 2012
Card SortingUsability Body of KnowledgeJune 1st, 2009
Card sorting: a definitive guideBoxes and ArrowsApril 7th, 2004