Definitions for "Fundamental interaction"
The known fundamental interactions are the strong, electromagnetic, weak and gravitational interactions. These interactions explain all observed physical processes but do not explain particle masses. Any force between two objects is due to one or another of these interactions. All known particle decays can be understood in terms of these strong, electromagnetic or weak interactions.
(physics) the transfer of energy between elementary particles or between an elementary particle and a field or between fields; mediated by gauge bosons
In the Standard Model the fundamental interactions are the strong, electromagnetic, weak and gravitational interactions. There is at least one more fundamental interaction in the theory that is responsible for fundamental particle masses. Five interaction types are all that are needed to explain all observed physical phenomena.