A muhmal transmitter is mentioned by name but without a sufficient identifier when multiple known individuals could bear that name. This differs from a mubham person, whose personal name is omitted altogether and replaced by “a man” or “a shaykh.”
Muhmal example: “Aḥmad narrated to us,” when the reporter studied with two teachers named Aḥmad.
Mubham example: “A man narrated to me,” with no personal name supplied.
For muhmal, one determines which named individual is intended. For mubham, one first tries to discover the person's identity at all. These are distinct critical problems.