In wave mechanics and signal analysis, the first, second, and third harmonics represent the foundational frequency components of a complex periodic wave. The first harmonic is synonymous with the fundamental frequency, representing the lowest and strongest primary frequency of the wave. The second harmonic occurs at exactly twice the frequency of the fundamental, while the third harmonic vibrates at three times the fundamental frequency. Each successive harmonic adds specific mathematical complexity to the waveform shape, altering its acoustic timbre or electrical distortion profile depending on the system.