An attractive force caused by quantum -mechanical electron correlation.

Source

An attractive force caused by quantum-mechanical electron correlation. For example, a neutral spherical molecule (such as a single argon atom) has no charge and produces no external electric field, yet a pair of molecules has a distribution of electron configurations weighted toward those with lesser electron-electron repulsions; this creates a small net attraction.

Source

An attractive force between atoms or molecules caused by the numerous transient dipoles resulting from electronic superposition.

Source