Desmodromic has to do with valve control in the engine. With desmodromic control, no return springs are used and the engine relies on compression to seat the valves. This is a design used previously by Mercedes and others but became an integral part of the Ducati motorcycle engine. It allowed for much higher rpm and horsepower and immediately proved itself in racing. See the book, Ducati, for illustrations of the Desmo valve control system and a description of its operating principles.