What is the definition of the 7 states of matter?

Answer 1

There are four fundamental states of matter:

• Solid
• Liquid
• Gas
• Plasma

Solids become liquids via melting and back again by freezing (a term not only applicable to water).

Liquids become gases by evaporation and back again via condensation.

Gases become plasma via ionisation and back again via deionisation.

Some substances bypass the liquid phase by a process called sublimation and back again via deposition... dry ice (CO2) is a good example at normal temperature and pressure.

There are also non-classical solids like glasses, disordered crystals, liquid crystals, magnetically ordered and microphase-separated.

Low temperature states: superfluids, Bose-Einstein condensates, Fermionic condensates, Rydberg molecules, Quantum Hall states and Strange matter.

There are two high energy states called Colour-glass state and quark-gluon plasma.

There are several others at the limits of theoretical physics which don't seem relevant to your question.