Hydrophobic effect: The arrangement of molecules in a polar solvent (such as water) which causes the polar regions to be oriented outwards towards the solvent and the nonpolar regions oriented inwards away from the polar solvent. Can also be thought of as the tendency for water to exclude nonpolar (hydrophobic) molecules.

The roughly spherical structure of a micelle is due to the hydrophobic effect.

The bilayer nature of a phospholipid bilayer is due to the hydrophobic effect.