Easton's Bible Dictionary (1897)
Mentioned in Scripture only in Joel 3:2, 12. This is the name given in modern times to the valley between Jerusalem and the Mount of Olives, and the Kidron flows through it. Here Jehoshaphat overthrew the confederated enemies of Israel (Ps. 83:6-8); and in this valley also God was to overthrow the Tyrians, Zidonians, etc. (Joel 3:4, 19), with an utter overthrow. This has been fulfilled; but Joel speaks of the final conflict, when God would destroy all Jerusalem’s enemies, of whom Tyre and Zidon, etc., were types.
The “valley of Jehoshaphat” may therefore be simply regarded as a general term for the theatre of God’s final judgments on the enemies of Israel. This valley has from ancient times been used by the Jews as a burial-ground. It is all over paved with flat stones as tombstones, bearing on them Hebrew inscriptions.
Smith's Bible Dictionary (1863)
(valley of the judgment of Jehovah), a valley mentioned by Joel only, as the spot in which, after the return of Judah and Jerusalem from captivity, Jehovah would gather all the heathen, (Joel 3:2) and would there sit to judge them for their misdeeds to Israel. ch. (Joel 3:12) The scene of “Jehovah’s judgment” as been localized, and the name has come down to us attached to that deep ravine which separates Jerusalem from the Mount of Olives, through which at one time the Kedron forced its stream. At what period the name “valley of Jehoshaphat” was first applied to this spot is unknown.
It is not mentioned in the Bible or Josephus, but is first encountered in the middle of the fourth century. Both Moslems and Jews believe that the last judgment is to take place there. The steep sides of the ravine, wherever a level strip affords the opportunity, are crowded—in places almost paved— by the sepulchres of the Moslems, or the simpler slabs of the Jewish tombs, alike awaiting the assembly of the last judgment. The name is generally confined by travellers to the upper part of the glen.
Hastings' Dictionary of the Bible (1898)
JEHOSHAPHAT, VALLEY OF (valley of the judgement of Jehovah), a place named only in Joel 3:2, Deut 3:12. Three leading explanations have been given. That the valley referred to is the same as the "valley of Berachah," where the forces allied against Israel were defeated by Jehoshaphat. 2 Chr 20:16-26. This event took place 100 years before Joel, and may have given rise to this expression of the prophet. That the valley is that of the Kedron, east of Jerusalem. Jews, Mohammedans, and Christians have identified the Kedron with the Valley of Jehoshaphat.
The Mohammedans point out a stone on which they think the prophet will be seated at the last judgment, and medieval Christian tradition also indicated a stone on which it was then believed that Christ would sit at the judgment. The valley is a favorite burial-place, and some expect that the sides of the valley will move apart at the resurrection to afford room for a great assembly. d. This identification of Jehoshaphat with the Kedron is now generally regarded as based upon a misinterpretation of Joel.
That the name does not refer to any special place, but to either (a) the scene of great victories, as those of the Maccabees; or (b) the general judgment at the end of the world; or (c) the truth that God's persecuted people he will defend and vindicate.