The properties of hadrons are described by a theory called quantum chromodynamics (QCD).
QCD predicts that quarks and antiquarks bind into particles called mesons.
Potentially QCD also has bound states of just gluons called glueballs.
An important part of the field of hadronic spectroscopy are the attempts to solve QCD.
The properties of hadrons require the solution of QCD in the strong coupling regime, where perturbative techniques based on Feynman diagrams do not work.