A harmonic wave is a wave that undergoes simple harmonic motion as it travels. It can be described by the equation D(x,t)=Asin(kx-wt+φ), where D is displacement, A is amplitude, k is wave number, w is angular frequency, x is position, t is time, and φ is phase. The document provides examples of how to use this equation to calculate properties like wavelength, frequency, and acceleration of a harmonic wave traveling through different media. It also includes sample problems solving for these wave properties given values for variables like velocity, frequency, amplitude, and position over time.