Longitudinal Wave: A wave in which the particle displacement is parallel to the direction of wave propagation, such as sound waves in air. Transverse Wave: A wave in which the particle displacement is...Longitudinal Wave: A wave in which the particle displacement is parallel to the direction of wave propagation, such as sound waves in air. Transverse Wave: A wave in which the particle displacement is perpendicular to the direction of wave propagation, such as waves on a string or electromagnetic waves. Wave Equation: A mathematical formula that describes the propagation of waves through a medium, often expressed as v wave = λf , where f is frequency, and λ is wavelength.