1. A semistable meson produced either in a neutral form with a mass 264 times that of an electron and a mean lifetime of 8.4 × 10-17 seconds or in a positively or negatively charged form with a mass 273 times that of an electron and a mean lifetime of 2.6 × 10-8 seconds. also called pi meson. see table at subatomic particle.

1. any of three semistable mesons, having positive, negative or neutral charge, composed of up and down quarks/antiquarks.

1. a meson involved in holding the nucleus together; produced as the result of high-energy particle collision