Explain the terms 'fluids' and 'rigidity' in the context of states of matter.

(N/A) Liquids and gases are called $fluids$ because they have the ability to flow. Their constituent particles are free to move around.
In solids,the constituent particles have fixed positions and can only oscillate about their mean positions. This property is known as the $rigidity$ of solids.
Both these properties depend on the nature of the constituent particles and the intermolecular forces acting between them.