Unlimited Detail is a new technology that may one day replace how all games geometry is made. Currently all 3D models are made by a number of polygons. Each year to get more realism.. more number of polygons are put in the models and CPU/GPU upgraded to enable that. But Unlimited Detail tech replaces all that by removing the polygon concept all together than replacing all shapes with point cloud i.e. nearlly infinite number of edges/corners. and thus you get perfectly round shapes and muscles without edges.