Definitions for "In phase"
Keywords:  instant, peaks, polarity, wave, collide
When the peaks and troughs of two waves directly match each other they are said to be in phase. When "in phase" waves of the same amplitude collide, the result is a new wave with twice the amplitude of the original two. This kind of behavior is often called constructive interference.
When two or more waves of the same frequency have their positive and negative peaks occurring at the same time.
When two or more periodic, time-varying waveforms are simultaneously at the same phase angle and trending in the same direction.