In the same way we can have a mole of anything. Now, the only thing is a mole is usually used for very small things. For example, we can talk about a mole of protons, a mole of electrons, a mole of atoms, a mole of molecules. Because these things are very very small it usually doesn't make sense to say a mole of people because that's impossible. We can't have a mole of people because we only have 7 billion people in the world. So moles are used for very small quantities of something.