A subatomic particle composed of one quark and one antiquark is called a meson. Mesons are composite particles that are formed by a quark and an antiquark bound together by the strong nuclear force, which is mediated by the exchange of gluons. The quark and antiquark in a meson have opposite electric charges, resulting in an overall neutral charge for the meson.
Mesons come in different varieties depending on the types of quark and antiquark involved. For example, the pion (π) is the lightest meson and consists of an up quark and an anti-down quark (or a down quark and an anti-up quark). There are also mesons containing strange quarks (such as the kaon) or charm quarks (such as the D meson), and so on.
Mesons play an important role in the study of the strong nuclear force and the behavior of quarks within hadrons. They have specific properties and decay modes that can provide insights into the fundamental interactions of subatomic particles.