A memorandum (memo) is an informal, internal document used to convey a message within an organization. It should be concise and clearly state the purpose upfront. The standard parts of a memo include a heading with to, from, date and subject fields, an opening paragraph stating the purpose, a body with the main message and any relevant details, and a closing to end courteously without a signature. Memos aim to quickly communicate one main idea to busy recipients in a clear, direct and informal tone.