Definition of "Incidental" :
noun: an item that is incidental
noun: (frequently plural) an expense not budgeted or not specified
"He requested reimbursement of $7 for incidental expenses."
adjective: occurring with or following as a consequence
"Snags incidental to the changeover in management."
adjective: not of prime or central importance
adjective: (sometimes followed by to') minor or casual or subordinate in significance or nature or occurring as a chance concomitant or consequence