Occurs only in Genesis 2:12, where it designates a product of the land of Havilah; and in Numbers 11:7, where the manna is likened to it in colour. It was probably an aromatic gum like balsam which exuded from a particular tree (Borassus flabelliformis) still found in Arabia, Media, and India. It bears a resemblance in colour to myrrh. Others think the word denotes "pearls," or some precious stone.
These dictionary topics are from M.G. Easton M.A., D.D., Illustrated Bible Dictionary, Third Edition, published by Thomas Nelson, 1897. Public Domain, copy freely.
Easton, Matthew George. "Entry for 'Bdellium'". "Easton's Bible Dictionary".