Boyd’s Bible Dictionary:
(mound). (1) A rampart of Jerusalem (2 Sam. 5:9; 1 Kings 9:15). (2) Where Joash was murdered (2 Kings 12:20). (3) A Shechem family (Judg. 9:6-20).
Concise Bible Dictionary:
1. “House of Millo,” in connection with Shechem, apparently a family or clan (Judg. 9:6,20).
2. A part of ancient Jerusalem, though afterward said to be “built” by Solomon; it was repaired by Hezekiah. The name always has the article, “the Millo.” Various sites have been suggested for it, but its locality and its form are unknown (2 Sam. 5:9; 1 Kings 9:15,24; 1 Kings 11:27; 1 Chron. 11:8; 2 Chron. 32:5). In 2 Kings 12:20 Joash was slain in the “house of Millo, which goeth down to Silla:” this may be another place, though apparently it was in Jerusalem.
Jackson’s Dictionary of Scripture Proper Names:
a fill (earthwork)