Extreme Polyhierarchy

Compared to the physical world, one of the online world’s benefits is that items can live in multiple locations. Because websites can classify products and other content along multiple dimensions, they help users navigate locally to related items and provide faceted winnowing of a large product space into manageable shortlists that can satisfy the user’s main requirements.

via Top-10 Information Architecture (IA) Mistakes (Jakob Nielsen’s Alertbox).