<P> In physics, a state of matter is one of the distinct forms in which matter can exist . Four states of matter are observable in everyday life: solid, liquid, gas, and plasma . Many other states are known to exist, such as glass or liquid crystal, and some only exist under extreme conditions, such as Bose--Einstein condensates, neutron - degenerate matter, and quark - gluon plasma, which only occur, respectively, in situations of extreme cold, extreme density, and extremely high - energy . Some other states are believed to be possible but remain theoretical for now . For a complete list of all exotic states of matter, see the list of states of matter . </P> <P> Historically, the distinction is made based on qualitative differences in properties . Matter in the solid state maintains a fixed volume and shape, with component particles (atoms, molecules or ions) close together and fixed into place . Matter in the liquid state maintains a fixed volume, but has a variable shape that adapts to fit its container . Its particles are still close together but move freely . Matter in the gaseous state has both variable volume and shape, adapting both to fit its container . Its particles are neither close together nor fixed in place . Matter in the plasma state has variable volume and shape, but as well as neutral atoms, it contains a significant number of ions and electrons, both of which can move around freely . </P>

A state of matter that is not a fluid is