(N/A) Definition: Nitrogen,oxygen,and fluorine are highly electronegative elements. When they are attached to a hydrogen atom to form a covalent bond,the electrons of the covalent bond are shifted towards the more electronegative atom.
This partially positively charged hydrogen atom $(H^{+\delta})$ forms a bond with another electronegative atom. This bond is known as a hydrogen bond.
In short: Hydrogen bond is represented as $H^{+\delta} \dots X^{-\delta}$ (where,$X = N, O, F, Cl$ etc.).
It is represented by a dotted line.
Hydrogen bond can be defined as the attractive force which binds the hydrogen atom of one molecule with the electronegative atom ($F, O, N$ or $Cl$) of another molecule.
Normally,van der Waals forces are weaker than hydrogen bonds.
Hydrogen bond energy is approximately $40 \ kJ \ mol^{-1}$,while van der Waals forces are typically less than $10 \ kJ \ mol^{-1}$.