Definition of "incidental"

Loosely associated; of limited relevance except indirectly; only accidentally related.  examples

Existing tangentially, being a byproduct, a tangent, or a likely consequence.  examples

Occurring by chance.  examples

(physics, of radiation) Entering or approaching, prior to reflection (more frequently incident).  examples

Minor items, not further defined. Incidental expense.  examples

Something that is incidental.  examples