Hydrogen bonding is an attractive intermolecular interaction stronger than Vander Waals forces that exclusively occurs when the Hydrogen atom is sandwiched between two highly electronegative atoms N, O, or F, one to which it is covalently bonded and the other it attracts electrostatically.
The molecules are closely associated with the Hydrogen bonds shown as a dash (----).
Hydrogen bonding is responsible for molecules' physical, chemical, and biological properties.
Read more about Hydrogen Bonding.