Answer:
There are 2 types of fluids. Gas and Liquid.
The process in which a liquid changes into a solid is called freezing. The particles loses kinetic energy, therefore the forces of attraction at the nucleus of the particles pull the particles more closely together. When a liquid changes completely into a solid, the particles will be very closely packed, and cannot move freely at all. An example would be the freezing of water into ice.
The process in which a gas in changed to a solid is called desublimation, or deposition. Most elements have 3 states of matter (solid, liquid, gas). With that said, a gas usually condenses (loses kinetic energy, the particles becomes more closely packed) to become a liquid, before undergoing the freezing process to change into a solid. However, some elements can skip the liquid phase and directly become a solid. This is affected by the pressure exerted on the gas. Under high pressure, water vapour for example can desublime into ice without first becoming water. This is how snow is formed.