Test Pilot Heirachy, IMHO:
Maintenance Test Pilot - Fleet pilot with extra training to do maintenance tests (usually not at all critical)
Production Test Pilot - OEM pilot trained to do acceptance testing of type designed normal aircraft. Tests are similar to maintenance tests. Often writes the acceptance test procedures, and often tests new pieces of gear that do not affect fundamental airworthiness (radios, hoists, etc.).
Experimental Test Pilot - OEM or Military customer test pilot - Trained by OEM or military to fly unapproved newly built or modified aircraft, those mods can include those that affect airworthiness (transmissions, blades, structure, controls). These aircraft are usually the first of a series to be produced, so by nature their design is less radical than a "research" aircraft. The tests performed can be quite difficult, and can be hazardous, such as a structural demonstration to critical limits, or a height-velocity test. Note: Military test pilots do not often fly unapproved aircraft on envelope establishment flights, these are usually first flown by OEM pilots, the data reviewed by military engineers, and then flight clearance is given for mil pilots to fly within that envelope.
Research Test Pilot - Experimental TP who flies aircraft that have been modified or special built to examine new and unique properties where production is not anticipated for the design. Such aircraft are designated as X in their model series, if military, but can have other names if purely civilly funded. Such aircraft as the XV-15, XH-59, CarterCopter are examples.
Most manufacturers have the TP staff that meets these definitions, although the difference between Experimental and Research is blurry, and sometimes non-existant.