The term lipid comprises a diverse range of molecules and to some extent is a catchall for relatively water-insoluble or nonpolar compounds of biological origin, including waxes, fatty acids, fatty-acid derived phospholipids, sphingolipids, glycolipids and terpenoids (eg. retinoids and steroids). Most lipids have some polar character in addition to being largely nonpolar. Generally, the bulk of their structure is nonpolar or hydrophobic ('water-fearing'), meaning that it does not interact well with polar solvents like water. Another part of their structure is polar or hydrophilic ('water-loving') and will tend to associate with polar solvents like water. This makes them amphiphilic molecules (having both hydrophobic and hydrophilic portions).For microbiology and food research sphingosines, ceramides, gangliosides, phosphatidyl inositol phosphates were used.