Define "Wet heat" vs. "Dry heat" (therapeutic)

Two parts to the question – 1) Define wet vs dry heat. 2) Who cares?

Can somebody clearly define the difference between “wet heat” and “dry heat” in regard to heating pads and similar things? My massage therapist recommended “wet heat” and said that would include a thing containing buckwheat that you heat in the microwave. If it’s not actually wet then how is that “wet heat”? Is a hot water bottle considered “wet heat” or “dry heat”, since the water does not touch your skin?

Also, in regard to therapy and/or soothing for muscles/tendons/whatever, why does it matter if the heat is wet or dry? If it’s “wet heat” where no moisture is touching your skin, who cares if it’s wet or dry?

I think the difference may not matter, but one possible reason it could is that wet contact typically involves a much higher heat transfer coefficient than dry. Wet heat would tend to bring your skin rapidly to the temperature of the object you touch. Picture a graph of the temperature suddenly jumping to some fixed value. Dry heat would tend to keep gradually pushing your skin towards the temperature of some distant (and possibly quite hot) heat source without strongly drawing it to exactly that temperature. Picture a graph of temperature drifting upwards but also depending on other things like your circulation.

But I don’t know if this is why they care, and suspect it may not be that thought out.

Thanks Napier but I am going to bump this! This has been bugging me for years (believe it or not!).