Other forms: memos
A memo is a short written note passed around inside an organisation. Two paragraphs about the new parking rules, pinned up by the kettle or sitting in everyone's inbox on Monday morning.
It is short for memorandum, and the full word survives in official writing — a memorandum of understanding between two companies. The plural is memos, while memorandum takes memoranda or memorandums. A memo travels inside an organisation, from one part of it to another, which is what separates it from a letter going out. In law and government a memo can run for pages, so length is not the test — the test is that it is a record, written to be filed. Did you not get the memo? is a standing joke aimed at someone acting on information everyone else has already replaced.
1nounmemoA short written message circulated inside an organisation.
“A memo went round reminding everyone to lock their screens.”
synonyms: memorandum, circular, note
2nounnoteA formal written note recording an agreement or setting out an argument.
“She wrote a memo to the board explaining the delay.”
memo is a written message.
Also accepted in games: memorandum
Memo is memorandum with the tail cut off, the way office English shortens whatever it types every day. The long form is what you still put on a legal document; the short one is what you leave on a desk. Nothing else changed: the same word, the same job, fewer syllables.
a clipping of memorandum.
Etymology from Wiktionary, CC BY-SA