Despite the common misnomer of it being solely a term used in electronics, Solid State refers to the area of physics encompassing any and all properties and phenomenae involved with crystals. Note that because these analyses all depend on order within the crystal, polymers and similar substances that have reached their glass transition viscosity will not be described by Solid State Physics directly, but rather will be mostly described by way of Statistical Thermodynamics.
"Solid State" is commonly mislabelled as an electronics term because the properties that drive such things as vacuum tubes and diodes is derived via Solid State Physics, such as with electronic energy band theory, atomic bonds, and bulk work functions.