I thought that was quite a reasonable article explaining things in pretty simple terms, and they do clarify what they mean by gummy at the start.

It would of been nice if they'd shown another cross-section photo with the actual effect the extra coating makes, rather than just the soft and hard materials.



Tram is short for trammel, but it's more an American term, although I'm pretty sure I've got British engineering books from the 60s/70s that use the term Tram. It's certainly not a youtube thing, and usage is likely to be vary on locality as well. Just like Teaps, which are only used in Scotland.