Solid State Civilization

Describe SolidStateCivilization here.

I believe that the author means, by saying solidstate, that such a civilization is bound by the rules of gravity, the speed of light, energy dynamics and so on.

All states are bound by the speed of light and energy dynamics. Did he mean that most of such civilisation's artefacts are in solid state, rather than in liquid, gas or plasma states? As for gravity, the natural plasma objects (stars) can exist only because of it.

Maybe the author meant technology that has relatively few moving parts? I.e. based on fusion, manipulation of fields, etc.

It's a term from Ghost in the Shell. Basically, the "few moving parts" explanation is it; this is extended to include people, to the point where you could have a perfectly fine life never stepping outside of VR. It also extends to biology (lots of moving parts, lots of wasted energy), which is replaced by nanotechnology (not much wasted energy). It's something they aspire to, not something they've mostly achieved.