Good old taxo’s.
“Taxonomies may be thought of as hierarchies of categories to group and organize information to be found when browsing, or as a structured set of terms used to tag content so that it can be retrieved efficiently and accurately. Sometimes the same taxonomy may serve both purposes, and sometimes two different taxonomies are used, one for each purpose, for the same content or site. Taxonomies are not new, in fact there has been a lot written about them, including an informative series of six articles here in Boxes and Arrows by Grace Lau in 2015. An area that still needs to be better understood is exactly how taxonomies should be designed and implemented to be most effective.”