Someone who enjoys wrapping their arms around trees because of the intense love they feel for nature. Some tree huggers are partial to certain species of trees, some will take whatever tree lovin' they can get. Many will even chain themselves to their favorite tree in order to get closer to them. This is known as "second base" in the tree hugging world. Third base involves sap.

Also, a phrase used to refer to environmentalists, activists and god-damned hippies.