Longitudinal waves are a type of wave where the particles of the medium move back and forth in the same direction as the wave travels. This movement creates areas of compression, where particles are close together, and rarefaction, where they are spread apart. Sound waves in air are a common example of longitudinal waves, as they travel through the air by compressing and expanding air particles. In a longitudinal wave, the energy is transferred through the medium without the medium itself moving long distances. This means that while the wave travels, the individual particles only oscillate around their equilibrium positions. Other examples of longitudinal waves include seismic P-waves and certain types of ultrasound waves used in medical imaging.