a property of liquids in which the exposed surface tends to contract to the smallest possible area because of unequal molecular cohesive forces near the surface: measured by the force per unit of length
See surface tension in American Heritage Dictionary 4
surface tension
noun
A property of liquids arising from unbalanced molecular cohesive forces at or near the surface, as a result of which the surface tends to contract and has properties resembling those of a stretched elastic membrane.