A system for
diesel engines by which fuel under very
high pressure is distributed through a common line (called
common rail of course) to all the combustion cylinders. The
injection then involves nothing more than the
motor management deciding when and how far to open the injection gates.
With common rail one can achieve high pression diesel injection, which is definitely the stuff that you want in a diesel engine. Competition to common rail is provided by Volkswagen in the form of their proprietary pump injection system.
Common rail was devoloped by the Italian FIAT group (owners of Ferrari and other nice Italian car brands). FIAT sold the design to Bosch, who made it available to other car makers as well.