This simply means it was entombed in a sticky resin which was then fossilized. Tree resin differs from sap. Sap is liquid that carries nutrients (food) to the different parts of a tree. Resins are soft sticky substances secreted from a tree that scientist believe could be for protection or to attract something that it needs. Personally, I like to think of it as the tree's No. 2 (carbon dioxide being its No. 1).