What is the definition of phase?

The completely homogeneous and uniform state of matter is called phase

Explanation:

A system has a unique set of properties at a given time, which is called a state. The state of a system does not depend on its configuration, but only on its intensive properties; if any of them vary, the state of the system will change. The mathematical relationship between the properties that characterize the state of a system is called the state equation. The completely homogeneous and uniform state of matter is called the phase. The most common phases include gases, liquids and solids. A system can also be multi-phase, the most common being the one that contains a gas phase and a liquid phase, although some systems that contain several liquid and solid phases (two liquid phases; a solid phase and a liquid phase) are also important.