What keeps the drop hanging on the pipette?

Two forces act on the drop: the force of gravity, directed vertically downward, and the force of surface tension of the liquid, which is directed vertically upward. The force of gravity is balanced by the force of the surface tension of the liquid.
The reason for the appearance of the surface tension force is the liquid molecules that are on the free surface of the liquid. These molecules are in special conditions than the molecules inside the liquid. They interact with molecules of another substance, which fall into the sphere of molecular interaction.
Water molecules interact with the glass molecules of the pipette, and the force of intermolecular attraction arises. Water molecules stick to glass molecules.