The subatomic particle composed of one quark and one antiquark is called a meson. Mesons are a type of hadron, which are particles composed of quarks and held together by the strong nuclear force. The quark and antiquark in a meson have opposite charges, resulting in a net neutral charge for the particle as a whole. Mesons are short-lived particles and are involved in strong interactions. Examples of mesons include the pion (π), kaon (K), and eta (η) particles.