Sometimes we can refer to multiple elements together as being either homonuclear or heteronuclear. In homonuclear compounds, these are compounds composed of identical elements. So this would represent our diatomic and polyatomic elements. So we talk about H2, Cl2, P4, S8. These would be our homonuclear elements, or we can name them diatomic elements or polyatomic elements.
In heteronuclear compounds, this is when our compounds are composed of different elements. So a good example would be water, which is H2O, carbon dioxide, which is CO2. Ammonia gas is big with fertilizers, that's NH3. Also glucose, which we've talked about in the past, C6H12O6.
So just remember, elements can exist as either monoatomic, diatomic, or polyatomic elements, and then we can also refer to them as either homonuclear if all the elements are the same or heteronuclear if the elements together are different.