FLUID definition: a substance, as a liquid or gas, that is capable of flowing and that changes its shape at a steady rate when acted upon by a force tending to change its shape. See examples of fluid used in a sentence.
Fluids flow easily and take on the shape of their containers. All liquids and gases are fluids.
A fluid in medicine or biology refers to any liquid constituent of the body (body fluid), [6][7] whereas "liquid" is not used in this sense. Sometimes liquids given for fluid replacement, either by drinking or by injection, are also called fluids [8] (e.g. "drink plenty of fluids").
Fluid definition: A continuous, amorphous substance whose molecules move freely past one another and that has the tendency to assume the shape of its container; a liquid or gas.