General Science

  • noun a stage or part of a larger process


  • noun a period or part of something which takes place


  • State of illumination of the Moon or another celestial object as seen from Earth. Phases can be expressed as new, full, half, etc or in percentage terms – a full Moon is 100 per cent illuminated.



  • noun one part of a larger process


  • A major period in the life of an asset or project. A phase may encompass several stages.


  • Within a periodic phenomenon or process, a specified stage of progress. For instance, a moon phase.
  • For a given periodic phenomenon, process, or quantity, the portion of a complete cycle that has been completed, as measured from a given reference point. Two or more periodic quantities having the same frequency and waveshape that pass through corresponding values, such as maximas and mini-mas, at the same instant at all times are in-phase. While periodic quantities that do not pass through corresponding values at the same instant at all times are out-of-phase. A phase angle expresses the difference between the phases of two such quantities. Phase is usually expressed in degrees or radians, where a complete cycle is 360° or 2π, respectively. Its symbol is φ.
  • In a polyphase system, such as a three-phase AC circuit, one of the circuits.
  • In chemistry, a homogeneous region that can be observed and separated from another it is present with. For example, ice in water.


  • A physical state of matter such as gas, vapour, liquid or solid. Two or more phases are common in many foods, e.g. milk and cream contain two liquid phases, water and butterfat, whipped eggs contain liquid and gas phases, cooked meringue contains a solid and gas phase and some cake mixtures are very complex mixtures of phases.

Information & Library Science

  • noun a particular stage in the development of something


  • noun a stage or period of development


  • noun a specific stage in a planned or expected sequence of events

Origin & History of “phase”

Greek phásis (a derivative of the verb phaínein ‘show’, source of English phantom) meant ‘appearance’, and also ‘cyclical apparent form of a planet, moon, etc’. This was adopted into modern Latin as phasis, and it originally passed into English (in the 17th century) in the Latin plural form phases. Phase represents a new singular formed from this. The more familiar modern sense ‘stage in a sequence’ is a metaphorical extension of the astronomical meaning.