Definition of phase noun from the Oxford Advanced American Dictionary

        

    phase

     noun
    noun
    NAmE//feɪz//
     
     
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  1. 1a stage in a process of change or development during the first/next/last phase the initial/final phase of the project a critical/decisive phase the design phase His anxiety about the work was just a passing phase. She's going through a difficult phase. The wedding marked the beginning of a new phase in Emma's life.
  2. 2each of the shapes of the moon as we see it from the earth at different times of the month the phases of the moon
  3. Idioms
      in phase/out of phase (with something)
       
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    1. 1working/not working together in the right way The traffic lights were out of phase.
    2. 2 (physics) if two or more light or sound wave cycles are in phase, their high and low points occur at the same time; if they are out of phase, they occur at different times
See the Oxford Advanced Learner's Dictionary entry: phase