1A short written note or memo used to record things to remember; a brief memorandum or personal/business note.
会議の後で、決まったことを覚書にまとめておきます。
After the meeting I'll summarize what was decided in a memo.
出張の予定は覚え書に書いて机の上に置いておいた。
I wrote the business trip schedule on a memo and left it on my desk.
ちょっとした連絡事項はメールではなく覚書で回すことにした。
We decided to circulate small notices as memos instead of by email.
2A formal memorandum, especially in diplomatic contexts, recording agreements or understandings between parties.
両国は境界問題に関する覚書に署名した。
The two countries signed a memorandum regarding the border issue.
覚書の内容は外務省が公式に発表した。
The contents of the memorandum were officially announced by the foreign ministry.