Every definition I see of Van der Waals interactions claim that they are short-range, nonspecific interactions between two chemical species. What does "nonspecific" mean in this context?
The definition of the van der Waals force that I like (and apparently so too do the folks who have contributed to the Wikipedia article on the topic) is much more *specific about what is and is not a van der Waals force. This definition originates in the International Union of Pure & Applied Chemistry Compendium of Chemical Terminology
The van der Waals force
is the sum of the attractive or repulsive forces between molecules (or between parts of the same molecule) other than those due to covalent bonds, the hydrogen bonds, or the electrostatic interaction of ions with one another or with neutral molecules or charged molecules.
Thus, a van der Waals force is a catch-all term to include all other very weak interactions between atoms and molecules:
- Dipole-dipole interactions between permanent dipoles
- Dipole-induced dipole interactions
- Induced dipole - induced dipole interactions (London dispersion)
- $\pi-\pi$ stacking
- Halogen bonding
- Repulsive forces derived from atoms trying to be inside another atom's van der Waals radius (Steric strain and torsional strain)
There are 3 forces that could be named as van der Waals' force (see wikipedia article)
What is common between them? The common between them is that these interactions are electrostatic interactions between dipoles of different nature (permanent dipoles, induced dipoles). And electrostatic interaction is not specific: there is no space specificity, or chemical specificity.