Definitions of incidental:

• noun:   an item that is incidental
• noun:   (frequently plural) an expense not budgeted or not specified

  Example: "He requested reimbursement of $7 for incidental expenses"

• adjective:   (sometimes followed by `to') minor or casual or subordinate in significance or nature or occurring as a chance concomitant or consequence

  Example: "Incidental expenses"

• adjective:   not of prime or central importance
• adjective:   following as a consequence

  Example: "Snags incidental to the changeover in management"