In the process of exploring plasmonic systems I have quite often come across the description of cavities as Plasmonic cavities. What is the exact difference between a normal cavity and a plasmonic cavity? Are they both the same? Or is the physics of these two systems quite different?
As pointed out by @garyp, there is not enough context. I will take a guess. I think you are talking about light-matter interactions in the presence of certain metals such as gold/silver/aluminium. The point being that small, sub-wavelength, particles out of these metals can display resonant response. Hence the 'cavity'.
If I am correct, then the answer is no, there is nothing special. Plasmonic cavity is like any other resonant system. What is sometimes important is that in case of plasmonic systems, the electromagnetic field 'sits outside', i.e. it is mostly in air not in metal, which makes these cavitities good for sensing and altering the local density of states (Purcell effect)