A polymer is a long molecule that's made up of repeating units of some smaller molecule, sort of like beads on a string. Proteins are polymers of amino acids. Carbohydrates are polymers of sugars, except for simple sugars, which are just 1 or 2 sugars in a molecule.

Hydrophobic means: [hydro = water] + [phobic = afraid of] so hydrophobic molecules are 'afraid' of water. Think of oil and water - the oil molecules sit in a layer on top of the water and don't stay mixed with the water molecules.

Here's a link with info about waterproof mascara:

A polymer is a molecule which is made up of many repeating smaller molecules, like a chain formed from many links. The molecules that make up a polymer chain can either all be the same, like the common plastic polypropylene, or different, like your DNA which is made up of 4 different types of molecules (called base pairs).

Hydrophobic substances are substances that do not tend to mix or interact with water. For example, a liquid that is hydrophobic, like oil, will separate from water. Or, when water is placed on a hydrophobic surface, the water will form droplets instead of spreading out and wetting the surface. Some polymers are hydrophobic, and so some mascaras do include polymers that make them waterproof.

However, many mascaras also include different types of wax, which are also hydrophobic. Waxes are not usually considered polymers, since they often consist of a head group, with long, hydrophobic carbon chains attached to it. The atomic structure of this head group is different from the atoms that form the chain, which makes waxes different from polymers.