Addition or appendage; the act of adding something onto something else (often used in formal or technical contexts).
説明に図を付加して理解を助けた。
I added a diagram to the explanation to help understanding.
このサービスには月額の付加料金がかかる場合がある。
This service may incur an additional monthly charge.
付加的な条件が契約に含まれていた。
Additional conditions were included in the contract.