The amount of space (volume) the liquid occupies does not change (actually the volume does change but the change is very tiny). ... Liquids are always considered to be incompressible fluids, as density changes caused by pressure and temperature are small.

What does it mean to say that a fluid is incompressible?

A fluid in which the density remains constant for isothermal pressure changes, that is, for which the coefficient of compressibility is zero.

Which is incompressible fluid?

An incompressible fluid is one which does not undergo a change in volume for a large range of pressures. Thus, its density has a constant value throughout the fluid. In most cases, all liquids are incompressible.