Boyd’s Bible Dictionary:

(burnt up). A Hebrew word (Josh. 18:1818And passed along toward the side over against Arabah northward, and went down unto Arabah: (Joshua 18:18)), designating the valley of Jordan and the Dead Sea, and the depression through Arabia to the Gulf of Akabah.

Concise Bible Dictionary:

This occurs as a proper name only once in the AV (KJV) where it should read “the Arabah” (Josh. 18:1818And passed along toward the side over against Arabah northward, and went down unto Arabah: (Joshua 18:18)); but it occurs in many other passages where it is translated “a plain” or “the plain,” and is also translated “desert,” “wilderness.” It refers to the plain situated between two series of hills that run from the slopes of Hermon in the north to the Gulf of Akaba in the far south. It is in this plain that the Jordan runs, and in which is the Sea of Galilee and the Dead Sea, also called “the Sea of the Plain.” About 7 miles south of the Dead Sea the plain is crossed by some hills: all north of this is now called el-Ghor, but the plain south of it retains the name of the Wady-el-Arabah. This latter part is about 100 miles in length, and the northern part about 150, so that for nearly 250 miles this wonderful plain or valley extends.
It might naturally be thought that the Jordan had at some time, after running into the Dead Sea, continued to run south until it poured itself into the Gulf of Akaba. But this is not probable, for the Dead Sea is nearly 1,300 feet below the sea, and the southern part is from end to end higher than the Ghor. The width of the Arabah is in some parts about 15 miles, but further south not more than 3 or 4. The southern end is also called the Wilderness of Zin, and it was in this part of the Arabah that a good deal of the wanderings of the people of Israel took place, before they turned to the east and left the plain on their left.
There can be no doubt that scripture uses the name “Arabah” for the whole of the plain, both north and south. The northern part is referred to in Deuteronomy 3:1717The plain also, and Jordan, and the coast thereof, from Chinnereth even unto the sea of the plain, even the salt sea, under Ashdoth-pisgah eastward. (Deuteronomy 3:17); Deuteronomy 4:4949And all the plain on this side Jordan eastward, even unto the sea of the plain, under the springs of Pisgah. (Deuteronomy 4:49); Joshua 3:1616That the waters which came down from above stood and rose up upon an heap very far from the city Adam, that is beside Zaretan: and those that came down toward the sea of the plain, even the salt sea, failed, and were cut off: and the people passed over right against Jericho. (Joshua 3:16); Joshua 12:33And from the plain to the sea of Chinneroth on the east, and unto the sea of the plain, even the salt sea on the east, the way to Beth-jeshimoth; and from the south, under Ashdoth-pisgah: (Joshua 12:3); Joshua 18:18: and the southern part in Deuteronomy 1:11These be the words which Moses spake unto all Israel on this side Jordan in the wilderness, in the plain over against the Red sea, between Paran, and Tophel, and Laban, and Hazeroth, and Dizahab. (Deuteronomy 1:1); Deuteronomy 2:88And when we passed by from our brethren the children of Esau, which dwelt in Seir, through the way of the plain from Elath, and from Ezion-gaber, we turned and passed by the way of the wilderness of Moab. (Deuteronomy 2:8). In other passages, especially in the prophetic books, the plain in general may be alluded to. It extends nearly due north and south, but bears toward the west before it reaches the Gulf.

Jackson’s Dictionary of Scripture Proper Names:

the desert plain