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.