A term used by Tolkien to refer to the languages of Men, as opposed to the Elvish tongues, or those of the other races of Middle-earth. By far the most prominent Mannish language in Tolkien's works is Westron, also called the Common Speech.
Most Mannish names are 'translated' by Tolkien into real-life languages. The most known example is Westron, which is always translated into modern English. Secondly Rohirian which is translated into Anglo-Saxon.
Another example are the Northern Mannish languages, translated into Norse, exemplified by the names of the Dwarves.