Solid-state physics is the study of rigid matter, or solids, through methods such as solid-state chemistry, quantum mechanics, crystallography, electromagnetism, and metallurgy.
Because its particles are packed close together, a solid is rigid, doesn’t flow, and isn’t easily compressed. A solid is defined as a state of matter with a definite shape and volume. In contrast, liquids can change shapes, while gases can change both shape and volume.
Solid, one of the three basic states of matter, the others being liquid and gas. A solid forms from liquid or gas because the energy of atoms decreases when the atoms take up a relatively ordered, three-dimensional structure.