what does solid state mean exactly?

As opposed to vacuum or gas state.

Tubes were the electronic component of choice when transistors were invented. Tubes were also available in gassed form. Mercury tubes, etc. I would guess at this point that some form of inert gas was used for high power transmitter tubes, like they are used in high output lightbulbs (xenon, halon, etc.). I will look that one up if you would like.

Also, I guess one could look at it from the more technically correct form Thermionic Conduction. This means that heat was used to create an ion "cloud". It could also be looked at as an electron "gas" (Imagine my mini-me making quotation marks with his little fingers here).;)

With silicon, or germanium, or whatever other crystal or metal used, there is no need for a gaseous state.

Hence... solid state.

I think.;)