Define density, kinetic energy, fluidity,compressibillity

Fluidity:fluidity is a property shown by liquids and gases. It means tendency to flow. Liquid and gases can change their shapes when a force is applied externally. This is the reverse of rigidity.
Kinetic energy:kinetic energy is also called energy of motion since particles of matter always remaining motion, they have kinetic energy.
Density:density is mass per unit volume. Density means how compact a substance is. Solid, because their particles are tightly packed, occur smaller volume and have greater densities. Gases have particles which can move around freely and therefore they can occupy more volume therefore, gases have least density.
Compressibility: compressibility means reduction in the volume of a substance on applying pressure. Solids and liquid are incompressible. This is because there is very empty space between the particles of solids and liquids. For example, you cannot fill more petrol in your car petrol tank even if you apply pressure. On the other hand, gases are easily compressible on applying pressure. It is because there are large empty space between the particles of gases.