This is one of the hardest kind of simulators to define. It's a nebulous catch all and the devices may have no regulatory standing1 as a result there is no common specification. Synonyms: Part(s) Task(s) Trainer, Procedure(s) Trainer, Cockpit Procedures Trainer, Panel Trainer, Panel Simulator, Procedures Panel, Instrument Simulator, Cockpit Simulator
They are for teaching procedural operation of equipment. Sometimes that's cockpit equipment, for example you could have a trainer specific to a particular subsystem of the aircraft or a more general one representing all systems in a higher level capacity. These are a kind of interactive textbook in a way. Sometimes they will look like an actual cockpit complete with switches and dials and sometimes they're just software on a tablet computer. Usually they're somewhere in-between. Often you will see many flat panel touch screens arranged in a generic cockpit like layout. Typically these will have "no out the window" visual at all, although some do, even if it's limited.
These can be an important tool for familiarizing pilots and crew on a specific type of aircraft when using a real aircraft for familiarization would be unreasonable. These can also be useful for supplementing a more advanced simulator with a lower cost alternative. A high end simulator is a valuable resource and it can make sense to free up as much time in it as possible by having students use PTTs to learn the basics before hand.
There are regulatory standards which apply to some kinds of PTTs however many devices are non-conforming as their use is not dependent on regulatory approval. Devices that are approved in the US by the FAA would be generally Level 4 Flight Training Devices (FTD Level 4) or Basic Aviation Training Devices (BATD) although there are many Level 4 FTDs and BATDs which are good enough you wouldn't want to call them Part Task Trainers. There are also many PTTs which wouldn't qualify as Level 4 FTDs or BATDs as they may only simulate one system. ↩