What is The strong interaction?

The strong interaction binds quarks into nucleons and nucleons into nuclei. At $10^{-15}\,\mathrm{m}$ it is attractive and far stronger than the electric repulsion (thousands of newtons between nucleons); beyond a few $10^{-15}$ metres it vanishes: its range is about $10^{-15}\,\mathrm{m}$. It grips protons and neutrons alike and ignores charge.