Hydrophobic

The term hydrophobic (hydro="water", phobic="fearing") is used to describe molecules that will not interact with water. Such molecules can also be known as lipophilic (fat-loving). Hydrophobic molecules are usually neutral and non-polar and so will not dissolve in polar solvents such as water^[1]. Instead, hydrophobic molecules are inclined to group together to avoid associating with water^[2]. This is a key feature in the phospholipid bilayers^[3] of cell membranes. Examples of hydrophobic substances include fats, oils and alkanes. 

Hydrophilic molecules are able to interact with water through hydrogen bonding^[4].

References

1. ↑ Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, Peter Walter, (2008) Molecular Biology of the Cell, 5th edition, Page 620, New York: Garland Science
2. ↑ Jeremy M. Berg, John L. Tymoczko, Lubert Stryer (2007), Biochemistry 6th Edition, Page 28, New York: W. H. Freeman and Company
3. ↑ Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, Peter Walter, (2008) Molecular Biology of the Cell, 5th edition, Page 620, New York: Garland Science
4. ↑ http://www.biology-online.org/dictionary/Hydrophilic