The term ‘pathfinder’ refers to finding aids created by libraries, and often these include guides to genealogical materials found in their facilities. There are also pathfinder research guides for specific geographic locations, record types, and other topics.
Some of these are available in printed form when you visit a library. However, you'll find that a wealth of these are also found on many libraries' websites, usually in PDF format. These can be conveniently accessed from your home during times when the library is not open. They can help you learn in advance of a research visit what materials a library holds in their collections so that you can prepare yourself for a more effective research trip.
However, don't overlook the fact that they can also be collected from multiple library websites to form a convenient and inexpensive personal reference library.