Nuclear physics is the study of the composition, behavior and interaction of atomic nuclei and their constituent parts. It differs from particle physics in that it spans a lower energy range where nucleons and even nuclei are stable and interactions can generally be described in terms of nucleon and meson degrees of freedom instead of quark and gluon degrees of freedom.
The effective theory known as Quantum Hadron Dynamics (QHD) and Chiral Perturbation Theory are useful for some problems in nuclear regime despite being known to be incomplete. Nuclear physicists also study the transition region where QCD corrections become important but the theory is not fully perturbative.
Nuclear physics provides the basic tools for nuclear power engineering and nuclear weaponry, though most nuclear physicists are not-involved in either of these fields.