The half amplitude of a sine wave refers to the magnitude or value of the waveform at the point where it reaches half of its peak amplitude. In other words, it is the value of the waveform when it is halfway between its maximum and minimum values.
For a sine wave, the peak amplitude is the maximum displacement of the waveform from its equilibrium position. The half amplitude, as the name suggests, is half of that peak amplitude. Mathematically, if A represents the peak amplitude, then the half amplitude would be A/2.
The half amplitude is an important concept when analyzing and characterizing sine waves as it helps determine various properties such as the peak-to-peak amplitude, average amplitude, and root mean square (RMS) amplitude of the waveform.