1. A substance whose molecules flow freely, so that it has no fixed shape and little resistance to outside stress: "Capable of flowing freely like water."
2. A substance that is able to flow freely; a liquid substance: "Please check the fluids in the car's engine."
3. A non-solid state of matter in which the atoms or molecules are free to move past each other; such as, in a gas or a liquid.
4. Used to describe something that can change easily or that changes often: "Boundaries between the farms were very fluid."

The application of computer technology to make quantitative analyses and predictions concerning the behavior of fluids: The computational fluid dynamics predicts the behavior of fluids in motion and of the effects of movements around objects by using numerical methods.

A fluid in which the properties are altered by either an electric field (electrorheological fluid) or a magnetic field (ferrofluid).

1. A colloidal suspension of finely divided particles in a carrier liquid, usually an insulating oil, is which rheological properties are changed through an increase in resistance when an electric field is applied.
2. A class of liquid which stiffens into a semi-solid when subjected to a electric field.

Electrorheological fluids are commonly colloidal suspensions, and their stiffening under an electric field is reversible.

Under the electric field, electrorheological fluids form fibrous structures that are parallel to the applied field and can increase in viscosity by a factor of up to 105.

Lithium polymethacrylate is an example of an electrorheological fluid.

The scientific study of fluids in motion; such as, gases and liquids.

The distribution of fluids in the rocks of a reservoir, as influenced by the rock's composition, porosity, method of producing saturation, and the degree of moisture characteristics.

1. The scientific study of the mechanical properties of fluids (gases and liquids) in motion or at rest, including the observation, description, and mathematical computation of the behavior of fluids.
2. The experimental and mathematical-computational study of the mechanical behavior of fluids.

Fluid mechanics includes the transfer of heat and matter resulting from motion of the fluid, and the driving of the fluid motion due to differences in density which may be induced by temperature, as well as the effects due to temperature dependency of the constants of materials; for example, the viscosity.

3. The study of fluids and gases at rest and in motion which can be divided into hydrostatics, the behavior of liquids at rest; hydrodynamics, the behavior of liquids in motion; and aerodynamics, the behavior of gases in motion.

Hydrostatics takes into account the forces exerted by a liquid in all directions, not just the downward gravitational pull; such as, the upward force exerted on a submerged object that causes bouyancy.

Hydrodynamics is the study of fluid flow and fluid friction, or viscosity.

Aerodynamics is the study of the motion of gases which is most often applied to the study of air and the motion of solid bodies in it.

The science concerned with fluids, either at rest or in motion, and dealing with pressures, velocities, and accelerations in the fluid, including fluid deformation and compression or expansion.

The pressure exerted by a confined fluid in static equilibrium, equal in all directions and perpendicular to the surface confining it.

In transportation engineering, a conceptual model of traffic flow based on the behavior of fluids.

The intuitive power of this model is expressed in common terms; such as, "flow" and "bottleneck", but the "fluid-flow analogy" is also used to construct sophisticated models of traffic behavior.

The fluid separating the osseous and the membranous labyrinths of the inner ear.

A fluid composed of solid magnetic particles of subdomain size colloidally dispersed in a liquid carrier; used in inertial dampers, fluid-cooled loudspeakers, and ink-jet printing.

In physics, a flow that takes into consideration the energy lost by the flowing fluid through friction with the boundaries restricting its motion.