Phases of Matter

" Matter can exist in several distinct forms which we call phases. We are all familiar with solids, liquids and gases. Whether a substance is a solid, liquid or gas depends on the potential energy in the atomic forces holding the particles together and the thermal energy of the particle motions. The pressure on the subtance also has an effect on the phase."
Solid is one of the major states of matter. It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a gas does.
Liquid is one of the three classical states of matter. Like a gas, a liquid is able to flow and take the shape of a container, but, like a solid, it resists compression. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly constant density.
gas - the state of matter distinguished from the solid and liquid states by: relatively low density and viscosity; relatively great expansion and contraction with changes in pressure and temperature; the ability to diffuse readily; and the spontaneous tendency to become distributed uniformly.

 

On the Picture above you can see the three types of matter.