A memorandum (abbrev.: memo) was from the Latin verbal phrase memorandum est, the gerundive form of the verb memoro, "to mention, call to mind, recount, relate", which means "It must be remembered (that)...". It is therefore a note, document or other communication that helps the memory by recording events or observations on a topic, such as may be used in a business office. The plural form of the Latin noun memorandum so derived is properly memoranda, but if the word is deemed to have become a word of the English language, the plural memorandums, abbreviated to memos, may be used. (See also Agenda, Corrigenda, Addenda)A memorandum can have only a certain number of formats; it may have a format specific to an office or institution. In law specifically, a memorandum is a record of the terms of a transaction or contract, such as a policy memo, memorandum of understanding, memorandum of agreement, or memorandum of association. Alternative formats include memos, briefing notes, reports, letters or binders. They could be one page long or many. They may be considered as grey literature. If the user is a cabinet minister or a senior executive, the format might be rigidly defined and limited to one or two pages. If the user is a colleague, the format is usually much more flexible. At its most basic level, a memorandum can be a handwritten note to one's supervisor. In business, a memo is typically used by firms for internal communication, as opposed to letters which are typically for external communication.Dean Acheson famously quipped that "A memorandum is not written to inform the reader but to protect the writer". Charles Peters wrote that "bureaucrats write memoranda both because they appear to be busy when they are writing and because the memos, once written, immediately become proof that they were busy."