HR Of course, you know how to write a memo—chances are, you’ve written hundreds of them. However, May 21 is National Memo Day, which makes this the perfect time to highlight the finer points of impactful memo writing. Memos—short for the Latin word “memorandum” (translation: “it must be remembered”)—have existed since the late 1800s. Kingdoms used them. So did armies. Today, the memo is a professional communication used in business writing to convey internal company news.