Write a definition for fluid that incorporates time
into a model of solids and liquids.

Definition: Fluid that can act as a liquid or as a solid depending on the pressure applied on it.

Explanation:

A fluid that incorporates time in a solid and liquid model is a non-Newtonian fluid. This type of fluid can behave as a solid or as a liquid depending on the pressure that is applied on it. This is different from normal fluids that remain the same regardless of the pressure they are subjected to. In the case of non-Newtonian fluids, when submitted to pressure, they are presented as solids, but without pressure, they are presented as liquids. This feature can be seen even within the same system.