Fluid containing more than one phases at certain pressure and temperature conditions.
Each phase of the Multiphase Fluid is represented either by a pure substance or by a Fluid Mixture (see Multiphase Fluid vs Fluid Mixture).
The most popular multi-phase fluid are:
It is important to remember that multi-phase fluid may collapse to a single-phase state at certain pressure and temperature conditions.
For example, a 2-phase oil + gas fluid may degrade to single-phase state when pressure goes up above bubble point.
See also
Natural Science / Physics / Thermodynamics / Thermodynamic system / Phase