What is Hydrophilic–lipophilic balance?

The hydrophilic–lipophilic balance (HLB) of a non-ionic surfactant is, in Griffin’s scale, $20$ times the mass fraction of its hydrophilic part: low values (3 to 6) suit water-in-oil emulsions, high values (8 to 18) oil-in-water emulsions and detergents.