What is the difference between glidepath and glideslope? How would you define each, and the key differences?
Glideslope: describes the systems that generate, receive, and indicate the ground facility radiation pattern.
Glidepath: is the straight, sloped line the aircraft should fly in its descent from where the glide slope intersects the altitude used for approaching the FAF, to the runway touchdown zone.
They serve the same purpose for the pilot, the difference is buried deep in the implementation concepts and administration of the systems. I would almost call it a philosophical difference. They have different points of failure, failures and inspections being distributed vs centralized, ease of confirming correctness, that sort of thing.
A Glidepath is a 3D path calculated by RNAV equipment, most commonly a GPSS receiver. It is based on extrapolating the most recent series of coordinates to a predicted position then comparing that to a mathematical model of the intended path. If the receiver has the wrong map-model or math, then the path of that plane will be wrong even if the calibration of the satellite signals are correct.
A Glideslope is an inclined radio signal, it is not used for calculation, it is a physical signal that can be followed. The equipment indicates where the plane actually is at that moment relative to the signal without extrapolating any past positions. The receiver is not following a map-model, if the signal is not aligned then the slope that all planes follow will not be aligned even if the receiving instruments are correct.