1) The sap that comes out of a tree.
2) A really tall guy going for a pee.
3) The piss on a tree left over by a guy or many guys who've done their buisiness there.
4) An insult related to the words slut, skank, whore, biznatch, hoze-bag, etc.
Courtney is such tree piss, there's no guy who hasn't done her over atleast once.