Resin gathered from the mastic tree. Joseph's brothers (Gen. 37: 25) sold him to merchants whose caravan of camels conveyed this commodity. The reference in Jer. 8: 22 is to a medicinal balm, perhaps the gum of the balsam tree.
Citation styles are based on the Chicago Manual of Style, 15th Ed., and the MLA Style Manual, 2nd Ed..
"balm of Gilead." In A Dictionary of the Bible. Ed. W. R. F. Browning. Oxford Biblical Studies Online. Jul 31, 2015. <http://www.oxfordbiblicalcstudies.com/article/opr/t94/e203>.
"balm of Gilead." In A Dictionary of the Bible. , edited by W. R. F. Browning. Oxford Biblical Studies Online, http://www.oxfordbiblicalcstudies.com/article/opr/t94/e203 (accessed Jul 31, 2015).