* Element: An element is a pure substance consisting of only one type of atom. Phosphorus (P) is an element.

* Compound: A compound is formed when two or more different elements chemically combine in a fixed ratio.

* Molecule: A molecule is formed when two or more atoms (of the same or different elements) bond together.

In the case of P4, it consists of four phosphorus atoms bonded together. Since it's formed from multiple atoms of the same element, it's a molecule of the element phosphorus.