Why are liquids and gases called fluids while solids are rigid?

(N/A) Liquids and gases are called fluids because of their ability to flow. The fluidity in both of these states is due to the fact that the molecules are free to move about.
On the contrary,the constituent particles in solids have fixed positions and can only oscillate about their mean positions. Thus,solids are rigid. These properties depend upon the nature of constituent particles and the binding forces operating between them.