Which definition of van der Waals forces is correct?
van der Waals forces is not another name for London dispersion forces. In his answer, airhuff has given IUPAC definition for van der Waals forces.
London dispersion forces are the intermolecular forces that occur between atoms and between nonpolar molecules as a result of the motion of electrons in those atoms and molecules. They are induced dipole-induced dipole interaction, better described in following diagram:

These inter-atomic or inter-molecular forces are the weakest of van der Waals intermolecular forces. London dispersion forces got its name due to its discoverer, Fritz London (Ref.1). You can find some details of the distance dependence on London forces here.
References:

Fritz London, &quot;The general theory of molecular forces,&quot; Trans. Faraday Soc. 1937, 33, 8b-26 (https://doi.org/10.1039/TF937330008B).