You're right to be confused! This is a common point of misunderstanding. Here's why:

* Molecule: A molecule is formed when two or more atoms bond together. This applies to O2 because it's made up of two oxygen atoms.

* Compound: A compound is a molecule formed by two or more *different* types of atoms. Since O2 is made of just oxygen atoms, it doesn't fit the definition of a compound.

In summary:

* O2 is a molecule because it's formed by two atoms bonded together.

* O2 is not a compound because it's made of only one type of atom (oxygen).

Let me know if you have any other questions about molecules and compounds!