Business memos are formal written messages within an organization used to communicate information for a specific purpose. They can describe problems, request information, contain proposals, explain policies, and more. Memos allow organizations to communicate efficiently without meetings. Effective memos are clear, concise, focused on a single theme, and use an informal tone. Memos have a standardized format including a heading with date, recipient, sender, and subject, as well as an opening, body, and closing section. They differ from letters in that letters are for external communication while memos are for internal use and follow a specific format.