A memorandum or memo is a document or other communication that aids the memory by recording events or observations on a topic, such as may be used in a business office. The plural form is either memoranda or memorandums.
A memorandum may have any format, or 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. 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.
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." 
A specific type of memorandum is the policy briefing note (alternatively referred to in various jurisdictions and governing traditions as policy issues paper, policy memoranda, or cabinet submission amongst other terms), a document for transmitting policy analysis into the political decision making sphere. Typically, a briefing note may be denoted as either “for information” or “for decision”.
The origins of the term “briefing” lie in legal “briefs” and the derivative “military briefings”.
The primary purpose of a briefing note “for decision” is to support decision making – to “help (or sometimes influence) a decision-maker to make a better decision in a particular problem situation than he might otherwise have made without the analysis”.
As the communication mechanism of the policy analysis process, the briefing note should provide a coherent synopsis of a policy problem, identify different policy options for addressing the problem, articulate opposing perspectives and advocate a recommended option. The typical structure for a briefing note includes: a description of the proposed policy; relevant background information; a discussion of key considerations (including implementation concerns, financial considerations, stakeholder impacts, and possible unanticipated consequences), a summary of arguments for and against the policy and a recommended decision. Policy documents that start with a proposal and assemble an argument that position are more accurately referred to as a government white paper. A government green paper which raises a policy option and is meant to open a dialogue on the proposal is more similar in tone to a briefing note than is a white paper.
There is no universal standard for a briefing note, but it is generally understood to be a concise, coherent summary of a public policy problem with a clearly articulated logic for following a recommended course of action. ”Next to a political nose, and a logical brain, the most important skill of the good treasury [person] resides in [their] fine drafting hand. The concise, coherent and penetrating note is the final expression of all other talents.” In many Westminster / Whitehall governance settings, policy analysts are expected to analyze the issue and write the briefing note from a neutral public service perspective. However, the briefing note “for decision” must contain a recommendation, acknowledging that “to say anything of importance in public policy requires value judgments, which must be explained and justified”.