Hydrophobicity is the association of non-polar groups or molecules in an aqueous environment which arises from the tendency of water to exclude non-polar molecules.
Source:
PAC, 1997, 69, 1137. 'Glossary of terms used in computational drug design (IUPAC Recommendations 1997)' on page 1145 (https://doi.org/10.1351/pac199769051137)