A pressure wave or compression wave is a shock wave propagated by variation in matter density. Sound is a type of pressure wave. During Doctor Timicin's experiment to revitalize Beta Praxillus in 2367, Lieutenant Commander Data reported that pressure wave harmonics were dispersing after Timicin's modified photon torpedoes detonated within the star. (TNG: "Half a Life" ) In early 2370, the USS Enterprise-D used a particle beam to destabilize the photosphere of a star, creating expanding pressure waves that led to a solar fusion eruption, which destroyed a Borg vessel. (TNG: "Descent, Part II" )