Unlike gases, solids and liquids both consist of particles that are held close together and are not easily compressed. Because of this limited free space between the particles, solids and liquids are called condensed phases.
Solids and liquids are two of the three main phases of matter, the other being gases. All three phases can be composed of ions, atoms or molecules, but they are distinguished from one another by the arrangement of their particles and their behavior.
Although there is not much space between the particles of a liquid, they are able to slide past one another, making it possible for liquids to flow and take the shape of their containers. Solids differ in that they do not flow with ease due to their particles being fixed in a rigid volume and shape. The difference in the arrangement of the particles of solids and liquids is related to their kinetic energy. Adding heat to a solid can increase its kinetic energy and change its phase to a liquid.
Gas particles have a great deal of space between them, making gases easily compressible. The particles are capable of moving past one another and flow with ease. A gas inside of a container naturally takes on both the volume and the shape of that container.