Strong Nuclear Force
Definition
The most powerful force in nature — it glues quarks together and holds atomic nuclei together against proton repulsion.
Technical definition
The fundamental interaction binding quarks via gluon exchange (quantum chromodynamics). The residual strong force between nucleons overcomes Coulomb repulsion at ~1 fm range. It is ~100× stronger than electromagnetism but acts only over femtometer distances.
Example
Protons in a nucleus should blast apart from mutual repulsion — the strong force overpowers it at close range, which is why nuclei exist at all.
The strong force has two levels: the fundamental force between quarks (gluons) and the residual force between protons/neutrons (sometimes just called ‘the nuclear force’). Both are ‘strong interaction’ but they are not identical.