Hydrophilic literally means water-loving, which means that a substance interacts strongly with water (or other polar substances). When talking about hydrophilic surfaces, they are always covered by a mostly invisible water film. Most metals are hydrophilic, as are glass surfaces. Hydrophilic surfaces have contact angles to water close to 0°.
The opposite of hydrophilic is hydrophobic. The aim of plasma treatment is often to convert hydrophobic surfaces into a hydrophilic state, as then adhesives, lacquers etc. adhere better and an increase in quality can be achieved.