1. . 
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.
See: acoustic, amplitude variation with offset, body wave, converted wave, dilatancy theory, dilatation, discontinuity, elastic, elastic wave, interval velocity, Poisson's ratio, rarefaction, S-wave, seismic, shadow zone, shear, Snell's law, sonic, sonic log, transit time, wave