Uniclass groups information under tables like Systems, Products, Spaces/Locations, and Entities, and each item gets a short alphanumeric code (e.g. Ss_25_10 for a wall system) that stays consistent whether it's referenced in a drawing, a schedule, or a COBie handover file. It's most common on UK and Commonwealth projects, and pairs naturally with classification fields already built into Revit's family and material parameters.