What is vender wall force

Dear student 
Van der walls forces:

A weak attractive force between atoms or nonpolar molecules caused by a temporary change in dipole moment arising from a brief shift of orbital electrons to one side of one atom or molecule, creating a similar shift in adjacent atoms or molecules.

The van der Waals force is originated by the attraction between electron-rich regions of one molecule and electron-poor regions of another. The attraction is much weaker than a chemical bond.
The intermolecular is  

• Attractive and repulsive forces between interacting particles (atoms and molecules)

• Do not include ionic and covalent bonds

• Attractive intermolecular forces are known as van der Waals forces.

Regards