What is Viscous fluid ?

Hint: A fluid is a material that continuously deforms (flows) under an applied shear stress, or external force, according to physics. Liquids, gases, and plasmas are all examples of fluids. They are substances with a zero-shear modulus, or, to put it another way, substances that cannot withstand any shear force.

Complete answer:
A fluid's viscosity is a measurement of its resistance to deformation at a specific rate. It refers to the informal definition of "thickness" in liquids: syrup, for example, has a higher viscosity than water.A viscous fluid is a real fluid that flows with some resistance in the opposite direction of its flow. The resistance is called viscosity, and the fluid is viscous. For example – honey is viscous fluid.

When a viscous fluid is pushed into a tube, for example, it flows faster near the axis than near the tube's walls. Experiments show that in this situation, some tension (such as a pressure difference between the tube's two ends) is needed to keep the flow going. This is due to the fact that a force is needed to resolve the friction between the fluid layers that are in relative motion. The compensating force is proportional to the viscosity of the fluid in a tube with a constant rate of flow.

Note: In superfluids, zero viscosity only occurs at extremely low temperatures. Otherwise, the second rule of thermodynamics specifies that all fluids have positive viscosity; such fluids are referred to as viscous or viscid in technical terms. Pitch, for example, may appear to be a solid due to its high viscosity.