MD — common meanings and uses of the abbreviation

Primary senses

• Doctor of Medicine / medical doctor — a common academic degree and professional title (often written M.D. or MD) indicating a physician who holds a medical degree.
• Managing Director — a senior corporate or organisational title, commonly abbreviated MD in company directories and business contexts.
• .md and Moldova / Maryland — the Internet country code top‑level domain .md belongs to Moldova; MD is also the United States postal abbreviation for the state of Maryland.
• Markdown and file extension — plain text files using the Markdown lightweight markup language often carry the extension .md (or .markdown) and are common in software documentation.
• Roman numeral — MD represents 1,500 in Roman numerals (M = 1,000; D = 500).

Other notable uses

• Md — chemical element — Md is the chemical symbol for mendelevium, a synthetic element (atomic number 101) named after Dmitri Mendeleev.
• mD — milliDarcy — in petroleum engineering and geology, mD denotes milliDarcy, a unit of permeability.
• Muscular dystrophy — MD is commonly used as an abbreviation for muscular dystrophy in medical shorthand and advocacy contexts.
• Command and computing uses — in some command‑line environments, md is a command (or alias) for making directories; it also appears as an abbreviation in software and product model names.
• Sports and judging — MD can stand for Matchday in sports schedules or Majority Decision in combat sports results.

Origins and style

Some senses have historical roots: the medical degree traces to Latin Medicinae Doctor, the Roman numeral use is inherited from classical notation, and the chemical symbol follows IUPAC conventions. Technical meanings such as the .md domain and the Markdown extension emerged with the Internet and software development. Style variations (M.D. vs MD, .md vs MD) reflect regional and editorial preferences.

How to interpret MD in practice

To identify which meaning applies, look at capitalization, punctuation and the surrounding field. On a business card or company report MD commonly means Managing Director; in front of a physician's name it means Doctor of Medicine; at the end of a filename it most often denotes Markdown; and in scientific literature capitalization like Md signals the element mendelevium. When in doubt, consult nearby context or an authoritative source in the relevant field.