Minhag (Hebrew: מנהג "custom", pl. מנהגים, minhagim) is an accepted tradition or group of traditions in Judaism. A related concept, Nusach (נוסח), refers to the traditional order and form of the prayers.
The Hebrew root N-H-G (נ-ה-ג) means primarily "to drive" or, by extension, "to conduct (oneself)".
The actual word minhag appears twice in the Hebrew Bible, both times in the same verse and rendered in this translation as "the driving":
The watchman reported, saying, "He has reached them, but has not returned. The driving is like the driving of Jehu [grand]son of Nimshi, for he is driving [his chariot] recklessly." (II Kings 9:20, Tanach: The Stone Edition)
Homiletically, one could argue that the use of the word minhag in Jewish law reflects its Biblical Hebrew origins as "the (manner of) driving (a chariot)". Whereas Halakha (law), from the word for walking-path, means the path or road set for the journey, minhag (custom), from the word for driving, means the manner people have developed themselves to travel down that path more quickly.
The present use of minhag for custom may have been influenced by the Arabicminhaj, though in current Islamic usage this term is used for the intellectual methodology of a scholar or school of thought (cf. Hebrew derech) rather than for the customs of a local or ethnic community.