Comment by Pet_Ant

How nucleons (neutrons and protons) are bound together is similar to a molecule. If they are close enough, they can 'share' their constituent quarks. You can calculate the interaction by a feynman diagram where the two nucleons exchange one quark in each direction. This is technically the same as one nucleon sending and the other absorbing a quark-antiquark pair, which is why physicists like to say that the nucleon attraction is transmitted by mesons (quark-antiquark pairs). Of course fundamentally the strong force still facilitates the whole interaction, as it's the one preventing nucleons from just falling apart into quarks.

That's the role the meson (a quark-antiquark pair particle) carries out, but I agree it's confusing. Here's a question from physics stack exchange (without any really clear answers, other than "go look up 'residual strong force'", not very helpful) that spells it out:

> "I just read somewhere that both gluons and mesons transmit the strong force, gluons between quarks inside hadrons, but mesons between nucleons. I thought that the strong force would have one field, and one associated particle, whether inside hadrons, or between nucleons"