Roughness corrected contact angle, is an angle where the effect of surface roughness is taken away.
Instead, one can measure static contact angles, advancing and receding contact angles, and roughness corrected contact angles.
Hydrophobic coatings are used in many consumers products. Contact angle measurements can be used to study them.
HMDS is used to render the surface of silicon more hydrophobic and thus to match better with the chemistry of the photoresist.