The gooey insides of a tree or plant. It's a liquid used to transport food and nutrients to all parts of the plant. Maple syrup, among other things, is made from tree sap. Old men from New England go out in the winter and tap maple trees to drain out the sap. No, silly, they don't tap them with their fingers--they stick a tap, similar to the one you'd use on a beer keg, into the tree, turn the spigot, and let it drain out into small buckets.

Also, a stupid, gullible person. These people are too much trouble during a party and should be ordered out of the house ASAP.