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

"Incidental expenses."