Phase, from the Greek phasis, meaning 'appearance', has a number of related meanings in English.

• The phase of a waveform is the position of any peak or trough compared to the same feature on a second waveform.
• A phase of matter is a physically distinctive form of a substance, such as the solid, liquid, and gaseous states of ordinary matter. Also sometimes included in this list are more exotic phases such as superfluids. Common examples of distinct phases within the same state of matter are immiscible liquids and the many phases of ice.
• A lunar phase is the appearance of the Moon as viewed from the Earth. Similarly with planetary phases .
• The audio effect and DJ and compositional technique of phasing.
• The term phase is used in small group communication , conflict, and negotiation to refer to segments during which the types of communication that occur remain approximately similar throughout, but clearly distinct from the types that occur during other phases.