What is the definition of semi formal letter?

A semi-formal letter is a type of correspondence that falls between formal and informal styles, often used for communication with acquaintances, colleagues, or individuals in a professional context where a personal touch is appropriate. It typically includes a greeting and closing that are less formal than a business letter but more structured than a casual note. The tone is respectful yet friendly, allowing for a balance between professionalism and personal connection. Examples include letters to a teacher, a supervisor, or a colleague.