Hydrophobic means water repellent.

A surface is hydrophobic, if the surface energy is smaller than the surface tension of water, i.e. smaller than 72 mN/m. Water does not spread on a hydrophobic surface but concentrates on spherical bubbles which do not wet the surface. By plasma coating ultra hydrophobe layers can be created.

Hydrophobity can create waterproof and self-cleaning surfaced.

The opposite of hydrophobic is hydrophilic.

Hydrophobic und hydrophilic surface treatment of fabrics