(n.) Geophysics. An elastic body wave or sound wave in which particles oscillate in the direction the wave propagates. P-waves are the waves studied in conventional seismic data. P-waves incident on an interface at other than normal incidence can produce reflected and transmitted S-waves, in that case known as converted waves. Syn: dilatational wave. See: Body Wave, Dilatation, Elastic, Rarefaction, Shadow Zone, Wave