Incompressible fluids are the imaginary fluids which are considered for the calculation of various factors associated with fluid dynamics. These fluids cannot change its volume due to any external pressures as the compressibility is assumed to be zero.
We know that,
1/K = dρ/(ρ dp) ( 1/K = 0 )
0 = dρ/(ρ dp)
dρ = 0
ρ = constant
It means that mass density will remain constant for incompressible fluids.
All existing fluids are compressible fluids. As compare to the gases, the liquids are considered as incompressible fluid where water is assumed as standard incompressible fluid.