备忘录 (bèi wàng lù): memorandum; aide-memoire; memorandum book

After every meeting, I write down the key points of the discussion and the next steps in a memo so I won't forget later.

She habitually keeps a shopping list in her phone's memo app; when she goes to the supermarket, she takes a look so she won't forget to buy milk and eggs.

The manager compiled the main terms of the contract into a memorandum and sent it to all department heads, asking everyone to confirm by Friday.

Before setting off on a trip, I wrote a memo reminding myself to bring my passport, charger, and regular medication, so I wouldn't discover at the airport that I'd forgotten something.