Nucleon is a term used in nuclear physics to describe a particle within an atomic nucleus, either a proton or a neutron. It is a useful term as many phenomena affect both particles in an identical manner, so in many cases they can be treated as equals.
Nucleons are spin 1/2 particles, fermions, interacting predominately by the strong nuclear force. The proton and neutron have very similar masses (around 0.1% difference), it is only the charge which differs, the proton being positive and the neutron being neutral. Therefore it is only the protons which interact via the electromagnetic force within the nucleus and this plays a minor role compared to the strong nuclear force.
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