special contract; special agreement; rider (insurance)
保険の特約で入院費用が補われた。
The hospitalization cost was covered by a rider on the insurance.
特約店でしか購入できない商品がある。
There are products that can only be bought at authorized dealers.
保険に特約を付けることで保障範囲が広がった。
Adding a rider to the insurance broadened the scope of coverage.