"Inter-" means between separate bodies/particles, within the macro scope.

Opposite of, "Itra-" meaning between constituents of a single body/particle, within the micro scope.

Therefore, "Inter-Action" refers to an action that takes place between 2 (or more) separate bodies.

As opposed to the theoretical "Intra-Action", which would refer to an action taking place between the constituents of a single body.

An example of celestial Inter-Action may be, the gravitational pull between a sun and the planets that revolve around it. Notice how the sun and the planets are separate celestial bodies, that are acting upon each other.

Examples of celestial Intra-Action may be: the atmospheric weather patterns, volcanic activity and tectonic drift experienced within a planet's exo-sphere; or the solar flares, nuclear fusion and convection experienced within a sun/star. Notice how these activities take place within the celestial bodies, but are the "Inter-Actions" of their constituents.

The prefixes "Inter-" and "Intra-" are really just references to scopes, relative to the scope of the topic, or of the body of topic. (For which in the above example, was "Celestial".)

"Inter-" means between separate bodies/particles, within the macro scope.

Opposite of, "Itra-" meaning between constituents of a single body/particle, within the micro scope.

Therefore, "Inter-Action" refers to an action that takes place between 2 (or more) separate bodies.

As opposed to the theoretical "Intra-Action", which would refer to an action taking place between the constituents of a single body.

An example of celestial Inter-Action may be, the gravitational pull between a sun and the planets that revolve around it. Notice how the sun and the planets are separate celestial bodies, that are acting upon each other.

Examples of celestial Intra-Action may be: the atmospheric weather patterns, volcanic activity and tectonic drift experienced within a planet's exo-sphere; or the solar flares, nuclear fusion and convection experienced within a sun/star. Notice how these activities take place within the celestial bodies, but are the "Inter-Actions" of their constituents.

The prefixes "Inter-" and "Intra-" are really just references to scopes, relative to the scope of the topic, or of the body of topic. (For which in the above example, was "Celestial".)