What is the name for fossilized tree resin?

Fossilized tree resin is called amber.

Amber begins as soft, sticky resin released by trees, often to seal wounds or defend against insects and disease. If the resin avoids decay and is buried by sediment, heat and pressure gradually drive off volatile compounds and transform it through polymerization into a stable fossil resin.

Amber can preserve insects, pollen, feathers, leaves, and other small organisms in exceptional detail. These inclusions provide evidence about ancient ecosystems, even though amber's chemical composition does not always reveal precisely which plant produced the resin. Amber ranges from pale yellow and orange to red, brown, green, and rare blue varieties.

Copal is the most common mix-up. It is younger, incompletely matured resin and is generally considered subfossil rather than true amber. Coal forms mainly from compacted plant material, while jet is a hard, black variety of fossilized wood. Amber has also been used for jewelry and ornamentation since prehistoric times.