Must the flow of compressible fluid is treated as compressible?

Fluid is the higher level designation for liquids (example: water = incompressible) and gases (example: air = compressible).Why is there such a difference in behaviour?Fluids can change their shape...

A fluid which is reduced in volume by an increase in pressure.

if the density of the fluid changes with respect to pressure is called compressible fluid f the density of the fluid does not changes with respect to pressure is called incompressible fluid

Incompressible - same as water.

No