Hydrophilic is the opposite of hydrophobic, which means that it is a property of a molecule that “attracts” water. No real attraction force is involved though. In general hydrophilic substances dissolve easily in water.
What is hydrophilic
Wikipedia‘s entry on hydrophilic says:
A hydrophilic molecule or portion of a molecule is one whose interactions with water and other polar substances are more thermodynamically favorable than their interactions with oil or other hydrophobic solvents. They are typically charge-polarized and capable of hydrogen bonding. This makes these molecules soluble not only in water but also in other polar solvents.
This simply means that a hydrophilic molecule posseses certain properties that allows it to interact very favourable with water molecules. More so then with hydrophobic substances like oil.
Both hydrophobic and hydrophilic
Some molecules have the characteristic of being both hydrophobic and hydrophilic, these can often be used as an emulsifier. Soap is a good example, which has a hydrophobic head and hydrophilic tail. This particular property allows it to mix very well with both oils and water, and can be used as a medium to mix water with oil.
Wax and hydrophilicity
Although the wax applied on a vehicle shows hydrophobic properties, the wax itself is very hydrophilic and actually becomes more hydrophilic after application. When a layer of wax is slightly worn, it can actually absorb water molecule. Seeing as wax is a sacrificial layer, this isn’t a real problem. It gives its life to protect the surface underneath, even if it means absorbing the dirt to prevent it from reaching the paint underneath. Some other coatings are hydrophilic in an emulsion, but become hydrophobic after the carrier evaporates.