Surfactant is short for Surface Active Agent

A surfactant is a compound which reduces the surface tension when dissolved in water or aqueous solutions or which reduces interfacial tension between two liquids of between a liquid and a solid.

Surfactants are usually organic compounds that contain both hydrophobic groups (their tails) and hydrophilic groups (their heads). Therefore, a surfactant contains both a water-insoluble (or oil-soluble) component and a water-soluble component.

Surfactants will diffuse in water and adsorb at interfaces between air and water or at the interface between oil and water, in the case where water is mixed with oil. The water-insoluble hydrophobic group may extend out of the bulk water phase, into the air or into the oil phase, while the water-soluble head group remains in the water phase.