Derived from the German word 'hügelkultur', the literal translation for a hügel mound is "hill culture". The design was originally pioneered by Sepp Holzer and involves developing what is effectively a raised bed, filled with rotten wood and materials that would otherwise go to waste to create a highly fertile soil.
A shallow pit is dug and layers of logs, brushwood or straw, wet leaves, compost, sod and soil are added to make a mound. As time passes the the layers slowly rot down, creating heat and nutrients that develop a rich soil for planting, and as the wood shrinks down more tiny air pockets appear, which in turn become self tilling. The mounds can be built between 2-7 ft tall (according to the zone you are working in), holding water and catching the sun, and providing fertility over many years with little maintenance.