I believe that what is being referred to here are molecules
with no dipoles
. This is where there is no overall separation of charge (a dipole moment
) across the molecule
Read literally the previous definition requires the atoms in the molecule to all be identical (no two elements have exactly the same electonegativity). For molecular elements (non-metallic) these consist normally of just two atoms.
However as long as the resulting molecule has no overall separation of charge (normally due to symmetry) then you can have non-polar molecules from a combination of different atoms (Carbon Dioxide and Methane spring to mind). The individual bonds in these are however polarised.