Special Purpose Simulators
Special purpose simulators are ones which can be used for a use which would normally outside what is offered in simulators of that type. Perhaps that use is usually limited to more advanced simulators which would otherwise be at a much higher price point, or is highly specialized and otherwise unavailable . There's often a high degree of overlap between special purpose and mission simulators.
For example a highly accurate autorotation1 simulator may be used to practice emergency situations in a helicopter, but may not be useable (or rated) to simulate other flight modes. In the case of autorotation it is generally possible on better advanced simulators, but the simulation may not be entirely accurate in simulators for which it wasn't a priority. In the US special purpose flight simulators may be approved by the FAA under 14 CFR 61.4.3 (c)
Obviously many aircraft are used to support activities other than just flying people between or around locations. Mission simulation can include many different things because people use aircraft for many diverse uses. Often it is quite important to simulate things beyond taking off, flying around and landing. Perhaps the mission is picking up an injured skier from the side of a mountain or hoisting a tree out of a selective logging site. Often it's simulating teams working together.
This can mean teams in the same aircraft such as the pilot and the operator of specialized equipment such as a hoist in the aforementioned search and rescue or logging operations. Or it could mean working with people on the ground, either real people in other simulators, or virtual people. There are simulators for helicopters and airplanes, trucks, construction equipment, ships, weapons systems, air traffic control towers, and just about everything else. Often it's important to be able to simulate many of these things working together.
For example one could have a "mission simulator" for training crews building a dam which would need to be able to simulate a helicopter picking up a load of concrete, and delivering it to the dam where it may be dropped into a vehicle controlled by another simulator who then delivers the concrete to pouring locations on site. By having the truck and helicopter simulator linked training the operators simultaneously will allow them to develop the skills needed work together safer and more effectively.