Refer to figures.
TURBOFAN ENGINE
A turbofan engine is the most modern variation of the basic gas turbine engine. As with other gas turbines, there is a core engine. In the turbofan engine, the core engine is surrounded by a fan in the front and an additional turbine at the rear. The fan and fan turbine are composed of many blades, like the core compressor and core turbine, and are connected to an additional shaft. All of this additional turbomachinery is colored green on figure 1. This type of arrangement is called a two spool engine (one "spool" for the fan, one "spool" for the core.)