UDH is short for Universal Derailleur Hanger. It is an attempt to standardize on one derailleur hanger design and eliminate hundreds of existing standards. Today each bike brand designs their own hangers, and may have multiple incompatible hangers across their own models. Multiply this by hundreds of bike brands and you have a very big problem when a rider breaks their hanger and has to find a replacement. The UDH is meant to simplify this. If a rider has a bike with a UDH compatible frame and they break their hanger, it means they will be able to go into almost any bike shop and pick up a replacement UDH hanger. Simple. Easy.
A license. The bike brand needs to sign up for a free license. The license gives the licensee the right to use the UDH patent and the UDH trademark. A bike brand may want to make their own slightly different derailleur hanger with different features. This is ok. However in order to mark their frames with the UDH trademark they must conform to UDH frame and hanger specification. This ensures that if a rider breaks their hanger, it can still be replaced with a standard UDH hanger.Apply for a license