an addition to something already present; an added item or supplement, often a note or comment appended to text or an explanation.
説明に付け加えがあるので、もう一度スライドを更新してください。
There's an addition to the explanation, so please update the slide once more.
彼の意見に一言付け加えたい。
I want to add a single remark to his opinion.
付け加えとして、参考文献一覧を末尾に載せた。
As an addition, I listed the references at the end.